Rust convert to enum Here's an example from the crate's readme: use subenum::subenum; #[subenum(Edible)] #[derive(Copy, Clone, Debug, PartialEq, Eq)] pub The num_enum and strum crates have a couple macros that might've worked for part of the solution, but I wasn't excited about bringing in 16k lines of dependency code for it. quinedot December 18, 2022, 10:19pm 4. Once set up, these conversions are straightforward and seamlessly integrate into the idiomatic ways of handling data in Rust. Integer constants can have a type suffix: Frankly I think you’ll find that such a prosaic implementation of FromStr on an enum is uncommon. This idea is also known as “Anonymous sum types”. If I didn't have a custom syntax I'm working with for the enum definition, and doing a couple other things there, I might have used the enum_map crate. Aside from wanting to remain on Rust 2018 stable, Convert vector of enum values into an another vector. The problem I'm trying to solve: In the clap crate, args/subcommands are defined and identified by &s Skip to main content Rust macro to convert between identical enums. But if the list is long Go to rust r/rust • by The derive macro defines a storage type [V; #enum_count] where #enum_count is the number of variants in this particular enum, as well as conversion to/from usize. Eg if the enum was to be referred to as entities, then the enum would be defined as enum entities {VIRTUALIZATION_NONE, VIRTUALIZATION_VM_FIRST,,,,}. I am This crate provides a macro to create a unitary enum and conversions from enum variants to a string representation and vice versa. Commented May 21, 2023 at 9:13. match self { ErrorCode::InvalidUsername => f. 24 fn example(s: &str) { let stream: proc_macro2::TokenStream = s. And if you intend to add enum types are integer types and you are allowed to assign any integer value to any integer object. The enum will have #[repr(<size here>)] with any of the unsigned integer types. let doe: Foo = 1. 1 Like. Enum Value Description; A: 0: The first value of the enum: B: 1: The second value of the enum: C: 2: The third value of the enum: In Rust, an enum is a type that can have multiple variants. So for instance, the following match statement is exhaustive: Why the wavefunction phases change under different environments? Reactivity of 3-oxo-tetrahydrothiophene Why would a brief power-down NOT Is there an easier way than manually creating a static array as described in In Rust, is there a way to iterate through the values of an enum? use Direction::*; static DIRECTIONS: [Direction; 4] = [NORTH, SOUTH, EAST, WEST]; Aren't enums suppose to be "enumerated"? I vaguely remember seeing an example before in Rust, but I can't seem to find it. 0 and references some items that are not present in Rust 1. Rust addresses conversion between custom types (i. std 1. E. If you don't completely understand the rules on unsafe coding in Rust, you should not be using unsafe code. Here's an example of what I want to do: As @VladFrolov has commented, there was an RFC proposed that would've added a method to the standard library, std::mem::replace_with, that would allow you to temporarily take ownership of the value behind a mutable reference. 0 (9fc6b4312 2025-01-07) In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe. What's the idiomatic way to convert from (say) a usize to a u32? For example, casting using 4294967295us as u32 works and the Rust 0. Enum in Rust is a type that allows you to define a set of named constants. There are third-party crates that provide similar functionality: take-mut and replace-with being notable ones I'm aware of. Customizing Enum Outputs. §Unsafely turning a primitive into an enum with unchecked_transmute_from If you’re really certain a conversion will succeed (and have not made use of #[num_enum(default)] or #[num_enum(alternatives = [. So you would need to check that the i32 matches one of the enum variants before doing the transmute. 0 How do I enable a struct instance to have fields with different types based on the enum value passed in? 1 Assign value to enum of struct type. I know (for some reason) that the input is always a Cat. – The Decodable instance created by #[deriving] is designed to decode the output of a #[deriving] Encodable instance; enums in particular work a bit strangely (they have to store which variant they are, and so aren't just the raw value of their contents). The serde_repr crate provides alternative derive macros that derive the same Serialize and Deserialize traits but delegate to the underlying representation of a C-like enum. enum ExampleEnum { A, B, C } fn main() { println!("{}", ExampleEnum::B as usize); } Is there a way to make a generic function that can take any data type that can do that? Or some Trait that encapsulates that functionality? Maybe in an "unsafe" way (transmute?) ? Converts strings to enum variants based on their name. As you guess, I am very new to rust. You have some relatively complicated rules for choosing which variant comes out of a value, so you will have While solving problem for day in AdentOfCode 2022 I thought to use From trait to convert color enums to numbers. The Piece constructor would take in an Option<PieceType>, Color and Piece would have methods to convert to and from the packed form. Where structs give you a way of grouping together related fields and data, like a Rectangle with its width and height, enums give you a way of saying a value is one of a possible set of values. MIT/Apache. I've been looking into a crate that provides a string representation of a unitary Enum (where the variants have no value) to allow parsing a string to an enum and vice versa. The as operator works for all number types:. : data[Person::John][Currency::USD] = 100; Is it possible to do with arrays and enums in Rust? The other problem is in fact that enums in Java are, well, enums (a collection of named constants), while enums in Rust are really tagged unions or, alternatively, algebraic data types. Strum also allows you to customize the output of your enum using the Display trait. Conversion. 0" strum_macros = "0. And you'll probably want to return Option<Test> or something because there are numbers which are not valid in that enum. What options do I have? The documentation tells me that I should implement the FromValue trait: Cargo. From my perspective (which may be colored by interacting with C a lot) conversion of integers to (field-less) enums is a frequent operation. Thanks for the link. The following naive code does not work: match b { Foo::Doe as u8 => Foo::Doe, } How is one supposed to easily match all enum variants? §Conversion. 1. enum PacketType { Connect, Ping, ChangeKeys { cipher_key: Vec<u8>, I am using nothing but rmp in this case. cisaacson asked this . Add conversion to and from underlying integer type on enums with the #[repr(u*)] or #[repr(i*)] attribute. But enums with only one variant are pretty much never used; a struct would do the job just fine. unwrap(), the hash map only ever returns the vector behind the key corresponding to the first enum variant. However, most applications eventually need to convert these enum values into human-readable strings for display or serialization purposes. In case anyone else is wondering about use self::Direction::*; that is there to bring the enum values into the A place for all things related to the Rust programming language—an open-source systems language that emphasizes performance, reliability, and productivity. I tried the following, but it seems not to work using contants in the match. The one caveat here being that if the underlying C library adds a new variant but the rust wrapper does not then users of the rust library are stuck. Rust unpacking the contents of an enum. 1, the compiler won't recognize that a particular variable can only be a particular variant of an enum at some point of execution. The following naive code does not work: match b { Foo::Doe as u8 => Foo::Doe, } How is one supposed to easily match all enum variants? A newtype enum is an enum where every variant wraps another type and the wrapped type can uniquely identify the variant. The opposite conversion is not always safe however. Nevertheless some implementations warn when you try to mix up different enum types. This is known as the discriminant. 0" strum = "0. As such, you always need to write an exhaustive match on it. This is useful when you need to store an enum in a database or pass it to a function that requires a number. You can use the as u32 syntax to convert an enum to a 32-bit unsigned integer. contains(List)? I can go through each enum item and do a. You can also implement a method that converts the enum to a boolean: enum Flag { One, Two, } impl From<Flag> for bool { fn from(f: Flag) -> bool { match f { Flag::One => true, Flag::Two => false, } } } One => true, Flag::Two => false, } } } Note that idiomatic Rust style uses UpperCamelCase for enum variants, and SHOUTING_SNAKE_CASE for Using the above implementation, the program will convert the string "tablet" into its corresponding Device::Tablet variant without complex pattern matching or conditionals. All Items; Derive Macros; Crate int_enum Copy item path source · [−] Derive Macros§ IntEnum. toml [dependencies] mysql = "15. ToString(), out Enum2 outValue) ? outValue : Enum2. parse(). When an Enum variant doesn't have a value, it will be serialized as a String, otherwise it will be serialized as an object with the variant name being the key. kukubawkbawk March 14, 2023, 4:31pm 1. derive type macro give you the information about fields in enum/struct/union. I think the current requirement of num_enum is quite honest: the enum needs an explicit #[repr({integer})] annotation: That is also an excellent point. As you've probably guessed by now, the question is about Telegram bot API's sendMessage method. Similarly it's not possible to swap the variant type even in this simple case where there's no conversion involved: @TheOperator's comment is fair, although I will add that I find myself, for various reasons (like performance, or for flexibility with higher-order functions / closures) sometimes keeping a static mapping to an enum around, so personally I think this is still a nice approach. The problem is that there are values of u8 that don't correspond to any variants of the Byte enum, Rust enums are type-safe sum types. However, when you need to convert between different types and use num_enum::FromPrimitive; # [derive (Debug, Eq, PartialEq, FromPrimitive)] # [repr (u8)] enum Number { Zero, # [num_enum (default)] NonZero, } fn main () { assert_eq!( I have this enum type: enum Animal { Dog(i32), Cat(u8), } Now I have a function that takes this type as parameter. Cannot Convert enum to u8. 0" Wondering if there's a "proper" way of converting an Enum to a &str and back. Multiple deserializations can A place for all things related to the Rust programming language—an open-source systems language that emphasizes performance, reliability, and productivity. There's Debug print, but the Eg if the enum was to be referred to as entities, then the enum would be defined as enum entities {VIRTUALIZATION_NONE, VIRTUALIZATION_VM_FIRST,,,,}. There are two steps here: converting the string value to an enum variant such as Roman::M, and then converting the enum variant to a number. Lineage Rust:- Enums Published:- 2023-April-11th Link Translate How can I convert an Option of one type into an Option of another type in Rust? I managed to sketch this out in the Rust playground, but this is a lot of boilerplate code to do what seems like a common operation. Enums in Rust are not like enums in C: they must not have tag values not defined by the compiler. You cannot call write!() inside the fmt() function to substitute {} with self, as this macro calls exact same function, thus creating the infinite loop. I want to achieve Copying a &'static str (i. It's somewhat specific to enums: I actually want a and b move out by value because I'm changing the enum variant anyway. As far as "without match," that seems like a bit of an arbitrary requirement. enum ProductCategory{ Dairy, Daycare, BabyCare } fn main() { let product_categories = vec![ProductCategory::Dairy, ProductCategory::Daycare, ProductCategory::BabyCare]; } This to send over an api what all the possible value a user can select for a particular field. This is unacceptably tedious, and the need I want to read enums from a MySQL table, but I'm failing to convert the string enums from the table into real Rust enums. When ! is stabilized, we plan to make Infallible a type alias to it: That is, this conversion is whatever the implementation of From<T> for U chooses to do. mzurs January 30, 2024, 12:54pm 1. We invite you to open a new topic if you have further questions or comments. From to convert from the inner type and vice versa. . chars(). So to convert the C enum to Rust, just add a name tag, and remove the trailing ; – @Alvra, by macro_rules you can't know about enum fields. For two types A and B you can write the constraint A: From<B> or B: Into<A> both of which mean mostly the same, i. If you have an enum like this: enum HelloWorld { Hello, World } Hello and World are enum variants. But while using them in arithmetic operations the conversion doesn't pick up available trait implementations automatically. You still have to update that implementation each time you add to the Enum, but there is less boilerplate at the point of use. However there are more specific ones Working with enums in Rust can significantly enhance the readability and maintainability of your code. By deriving Display, you gain the ability to control how enums are printed, The other problem is in fact that enums in Java are, well, enums (a collection of named constants), while enums in Rust are really tagged unions or, alternatively, algebraic data types. – Masklinn. pub enum InteractionCode { MenuCharacterCreation { action: CharacterCreationAction }, // this was how i was doing it before, // but it's becoming cumbersome with so many interactions // especially with ones in different categories // the if i have an enum with different types like enum Number { I A place for all things related to the Rust programming language—an open-source systems language that emphasizes performance, If you have a case when a type conversion is appropriate and possible and I would like to store vectors of tuples of data and related callback functions inside a HashMap, and decide which vector to iterate over based on the current value (or variant) of a certain enum. Unknown; This will allow you to handle input values that don't exist in Enum2 without needing to call Enum. Rust has a built-in way to convert an enum to an integer, but not the other way. Just to know is it possible to convert any given enum directly to String? kornel January 30, 2024, 12:58pm 2. A place for all things related to the Rust programming language—an open-source systems language that emphasizes performance, reliability, and productivity. However, some Rust developers have been considering making it such that each enum variant would be its own type, which would be a subtype of the enum itself. How to read a value of an enum which associates with a custom type in Rust? 0 How do I enable a struct instance to have fields with different types based on the enum value passed in? As this is naturally exhaustive, this is only supported for FromPrimitive, not also TryFromPrimitive. If the conversion function takes E1 by reference, it can't construct the E2::B and E2::C variants. Currently, discriminants are only allowed to be integers, not arbitrary types like &'static str, although that may change in the future. 0" serde_json = "1. It therefore provides an alternative to the built-in `#[derive(FromPrimitive)]`, which requires the unstable `std::num::FromPrimitive` and is I have an enum with two variants: enum DatabaseType { Memory, RocksDB, } What do I need in order to make a conditional if inside a function that checks if an argument is DatabaseType::Mem This crate is a procedural macro implementation of the features discussions in rust-lang/rfcs#2414. The answers still contain valuable information. ])] for any of its variants), and want to avoid a small amount of How to convert an enum variant into u8 in Rust? Ask Question Asked 1 year, 7 months ago. There is no guarantee what they end up compiling into, with a few rare exceptions (Option<&T> for example). Another case that is valid is if it is known that no new variants From my perspective (which may be colored by interacting with C a lot) conversion of integers to (field-less) enums is a frequent operation. By deriving Display, you gain the ability to control how enums are printed, This topic was automatically closed 90 days after the last reply. If I change the definition of actor so that actions be Vec<String> instead of Vec<Actions>, it produces valid TOML. 1 If you have an enum with only one variant, you could also write a simple let statement to deconstruct the enum. Ask Question Asked 3 years, 8 months ago. e. Rust macro to convert between identical enums. While tagged unions can represent plain enums easily, the converse is not true. I To explicitly convert an integer to our AtomicNumber enum, we can write a conversion function that takes an unsigned 32-bits integer as parameter and returns an Convert number to enum. In Rust we have the trait From in the standard library and its companion Into. However, if you don't need the full range of char for the key and you don't If you have many enums which you want to print, you can write a trivial macro to generate the above implementation of Display for each of them. contains(List::Rather) || a. Patterns in let and match statements must be exhaustive, and pattern matching the single variant from an enum is exhaustive. And because we assign integer value to these variant, we can use as keyword to convert enum variant to integer type. Note that after wrapping all variants in Arc, you no longer need to wrap the enum itself, because the enum will get Arc properties (cheap cloning) simply by deriving Clone. The latter can be accomplished by employing the cast operator. play. A deep copy of the string would be a clone and would be typed as a String. 2 How to convert a string to an enum? 2 How can I return a &str from Strings in an enum in a method impl? 7 open_enum will generate a debug implementation that mirrors the standard #[derive(Debug)] for normal Rust enums by printing the name of the variant rather than the value contained, if the value is a named variant. An enum in Rust is not intended to be used as bit flags. write_str("Invalid user name"), In this particular case, what I want to do is have an enum which may have different types wrapped as a generic parameter class to create strongly typed query parameters in a URL, though the specific use case is irrelevant, and return a conversion of that wrapped value into an &str. However, this requires me to specify the assigned values now multiple times i. I'd like this parse_mode to serialize as a string depending what it is: if it's Markdown then serialize to "parse_mode": "markdown" This enum has the same role as the ! “never” type, which is unstable in this version of Rust. You don't have to define the values, by default in Rust enums will count up their discriminant from 0 and you can implement From in terms of as to get the desired semantics – cafce25. The answer was to use serde's flatten macro for the file_or_folder that did not exist in the raw data, but was built using a combination of fields in the raw data (per the serde docs for Pagination, where the raw data does not have the key pagination, but the values to construct Pagination). The first can be achieved by implementing FromStr for your enum. PublicFlags can only take the values given in the enum (and not a combination). rs. Answered by adamreichold. Every variant of an enum is assigned to a single integer value. Rust does not. Modified 1 year, 7 months ago. Summary. Enums in rust are algebraic sum types. . However, when I try to call hashmap,get(&enum_variant). It provides developers with tools to handle text representation in a clean and efficient way. Motivation. We will go from int to enum. Rust, Conversion between Enum and Integer. 15. If you want to be able to convert your I'm writing a procedural macro to convert the variants of an enum into individual structs and implement some traits for that struct. In the example below there there is a reusable function called any_as_u8_slice instead of convert_struct, since this is a utility to wrap cast and slice creation. By the end of this article, you will have a solid understanding of how to convert Rust enums to integers. enum_str-0. enum ExampleEnum { A, B, C } fn main() { println!("{}", ExampleEnum::B as usize); } Is there a way to make a generic function that can take any data type that can do that? Or some Trait that encapsulates that functionality? Maybe in an "unsafe" way (transmute?) ? I am wondering how to implement a method for any enum that will return the variant identifier as a String or &'static str, without using any external crate. Well, it seems the toml crate has the same questions I do: how do you serialize the enum? When I create an actor and use toml::to_string() on it, it produces the output Err(UnsupportedType). enum Foo { Bar, Doe, } I want to be able to create an instance of Foo via e. Commented Aug 6, 2021 at 8:07 I want to read enums from a MySQL table, but I'm failing to convert the string enums from the table into real Rust enums. Derive macro for conversion between integer and enum. Rust----Follow. You can use the newtype_enum attribute macro to define a newtype enum. The generic conversions will use the From and Into traits. Rust website The Book Standard Library API Reference Rust by Example The Cargo Guide Derive Macros; Crate enumn Copy item path source · [−] Expand description Convert number to enum. Indeed, only in this specific case. This can be overridden using serialize="DifferentName" or to_string="DifferentName" on the attribute as shown below. So an EnumMap<K, V> is just an array of Vs that Sure. So an EnumMap<K, V> is just an array of Vs that Rust, Conversion between Enum and Integer. I'm trying to convert an unsigned integer to an enum. rust-lang. 0. 0" serde_repr = "0. The generated function is named In this quick post, we will cover how to move between enums and integers in Rust. #[enum_derive] As of Rust 1. This is valid and no diagnostic is required by the Standard. contains(List::Long) etc. Here is example code. Unfortunately, in Rust reflective programming is somewhat difficult. This crate provides a derive macro to generate a function for converting a primitive integer into the corresponding variant of an enum. 2. ADMIN MOD Casting i32 to enums . Skip to main Implementing Generic Trait for Enum in Rust. Modified 3 years, 8 months ago. Instead, you should use the parameter of the function f: &mut fmt::Formatter to write the result you want. #[derive(FromPrimitive)] pub enum QoSHistoryPolicy { } impl From<rmw_qos_history_policy_t> for QoSHistoryPolicy { fn from(x: rmw_qos Declare your own custom enum with all errors your application works with (or one subsystem of your application; granularity highly depends on the project), and declare From conversions from all errors you work with to this enum type. into(). I guess you could create an array containing every enum value and iterate over it checking for equality. This library provides the following attribute macros: #[auto_enum] Parses syntax, creates the enum, inserts variants, and passes specified traits to #[enum_derive]. in the From for enum -> int implementation and in the TryFrom implementation for int -> enum Rust allows you to convert field-less enums into an integer type using the as operator. In Java-like languages ADTs are usually modeled with class hierarchies. Both approaches leverage very popular crates. IsDefined or catch ArgumentExceptions thrown by Enum. So to convert the C enum to Rust, just add a name tag, and remove the trailing ; – ただ、C++のenumはコードコメントに記載した通り、範囲外の値であることのチェックはありません。 Rustのenumでは範囲外の値でないことのチェックが必須となる点がC++のenumと異なります。 以下では概要で述べた3つのやり方を順に説明します。 I have tried #[repr(u8)] and adding pub to the enum. Therefore I don’t think that it would be a useful thing to have. Why Convert Enums to Strings in Rust? Enums are a great way to model various states, options and categories in a Rust program and provide type-safety. Strings. For example -1_i8 as u8 is lossless , since as casting back can recover the original value, but that conversion is not available via From because -1 and 255 are different conceptual values (despite being How to match the enum and replace it in some branches using some parameters in the new variant? Rust matching on enum members behind mutable reference. 12 reference docs on type casting say Using the Display and ToString traits for string conversion of enums in Rust is a powerful mechanism. I used to derive FromPrimitive to be able to convert int types like u8 to my enum, how do you perform that now that What @SvenMarnach wrote is probably the way to go, simple and effective. Converts strings to enum variants based on their name. The enum contains many types, some are structs, others are String or numeric types Convert Rust enum with many types to PyAny #2652. Convert number to enum. This is so that certain optimization options are open in the future. Aside from strum, you could also implement this without match by creating a global HashMap<String, T> for each enum type T and having the From implementation just do a lookup on that map. It is the reciprocal of `TryInto`. Beware, if the enum values change later and x >= Rank::Ace as u8 && x <= Rank::King as u8 no longer guarantees that the value is a valid enum value, undefined behavior will result if a bad value is converted. It is not necessarily limits to generating methods for the enum itself. In Rust, names are just some display utility for us mere humans, the B in MyEnum<u32> and MyEnum<String> may happen to have the same visual representation, but they are completely different syntactic entities as far as the language This subreddit is for asking questions about the programming language Rust Members Online • garma87. To silent the warning the best is to not mix up the enum types, but otherwise I would recommend to cast it to the One option is to implement the Deref (and/or DerefMut) trait to convert to the common part. You can use the crates enum_derive and custom_derive to do what you Use num_derive and num_traits. The code snippets provided both work for what I'm trying to do, but I was looking to see if there was a way to generally convert literals -> enum that would ideally be short and work for an arbitrary number of enum values. How do I match enum values with an integer? has a discussion on this. You can also generate custom functions if you wanted to. help. #[derive(Debug)] enum ParseMode { Markdown, HTML, } Tip. That’s why using a proc macro instead can be useful. It is possible in rust to cast enum types to numbers using "as" like so. For example, we may want to say that Rectangle is one of a set of possible shapes that also includes Circle and Triangle. Now what this “can be converted” means is not 100% clear and basically the authors of the types A and/or B decide what it should mean, but it This is wildly unsafe, and can trivially cause undefined behaviour. You have to write a second match. g. ADMIN MOD Integer to enum after removal of FromPrimitive . Some common cases where you need enum-string conversion are: In short: you want to convert 1 an u8 value to an Byte's variant. enum_str 0. 84. Each variant of the enum will match on it’s own name. 14. Multiple deserializations can Also, for completeness sake: The basic form [] has a numeric value of an unsigned positive number starting from 0 (at least, for this specific case). However, it was not accepted. This is usually accessed via the parse method on &str. ztgoto September 23, 2021, 6:38am 1. This subreddit is for asking questions about the programming language Rust Members Online While solving problem for day in AdentOfCode 2022 I thought to use From trait to convert color enums to numbers. nayru25. Primitive types can be converted to each other through casting. This is unacceptably tedious, and the need Is there an easy way to format and print enum values? I expected that they'd have a default implementation of std::fmt::Display, but that doesn't appear to be the case. If &'static str is too verbose for you, you can always define a type alias. I have tried #[repr(u8)] and adding pub to the enum. Rust has a common trait for converting strings into values when that conversion might fail: FromStr. Say I have struct Data; enum State { First(Data), Second(Data, Data), } And I want to add a method to it converting First to Second: impl State { fn convert(&mut self, extra_data: Data) { } } If Data is not constructable in impl State scope, this is impossible in safe Rust (right?). And I can see two options: Add a placeholder variant to State: enum State { Empty, Here is a version that uses Enum. I am new to Rust, so it is entirely possible that I'm trying a completely wrong approach, so please suggest a better one if necessary :) Say, I'm writing a CPU emulator, and I want to organize functions that implement assembly instructions in a nice and convenient way, by using enums to define instructions and their addressing mode variants. 2. Derive FromPrimitive using the num crate to obtain the missing piece. proc_macro2::TokenStream use proc_macro2; // 0. enum Suit { Heart, How do i access enum values in rust when I Ah sorry, I understand your motivation for wanting enum variants as types, that'll be a great feature. – Is there a stable way to convert rust enum types to strings (and from strings to enum types) without the use of std or fmt? The reason I am asking is because std appears to account for and 'bloat' the final binary size by around 33% (using cargo bloat) - leaving me with an executable almost 1MB in size for some very simple code. 1 Perform Rust type conversion without unwrapping Option Is there a stable way to convert rust enum types to strings (and from strings to enum types) without the use of std or fmt? The reason I am asking is because std appears to account for and 'bloat' the final binary size by around 33% (using cargo bloat) - leaving me with an executable almost 1MB in size for some very simple code. Something like: pub enum MyEnum { EnumVariant1 EnumVariant2 } impl MyEnum { fn to_string(&self) -> String { // do Rust stuff here } } Using the above implementation, the program will convert the string "tablet" into its corresponding Device::Tablet variant without complex pattern matching or conditionals. 4. This may or may not be faster depending on how many variants there are, and how efficient the code Background In this quick post, we will cover how to move between enums and integers in Rust. How to check if &str contains enum in Rust? 0. The enum Test { A, B, } fn convert(n: u8) -> Test { todo!(); } { A, B, } fn convert(n: u8) -> Test { todo!(); } The Rust Programming Language Forum Convert from number to enum. 0. Rust does not provide reflection and usually use #[derive] for that kind of tasks. This allows C-like enums to be formatted as integers rather than strings in JSON, for example. – You forgot that enum variants are not types - you need to introduce wrappers in order for an enum to be able to contain other enums: enum Event { WebEvent(WebEvent), KeyEvent(KeyEvent) } The rest is pretty straightforward: Serialize enum as number. Note that the question asks about converting, this example creates a read-only slice, so has the advantage of not needing The conversion is value-preserving: the conceptual kind and meaning of the resulting value is the same, even though the Rust type and technical representation might be different. Rust proc_macro_derive (with syn crate) generating enum variant for matching. 2 Rust website The Book Standard Library API Reference Rust by Example The Cargo Guide Clippy Documentation enum_ str 0. BTW, moving from enum to ints is a relatively more straight forward operation. Tryparse: Enum2 value2 = Enum. nth(n as usize). #[derive(Debug, Deserialize)] struct Rust website The Book Standard Library API Reference Rust by Example The Cargo Guide Clippy Documentation int_enum 1. The second one, there are many ways, but you could do it with an impl From<Roman> for u32 for example. copying the reference only) has no cost. I'm open to I'm working with Diesel library and Sqlite database, trying to create Rust enum which saves to database as diesel::sql_types::Text, but even with example code it doesn't work as it should. 34 and above, std::convert::TryFrom<&str> will be derived as well). There's a crate called subenum that has a derive macro for automating the creation of the SubEnum and the conversions From<SubEnum> for SuperEnum and TryFrom<SuperEnum> for SubEnum. The generic conversions will use the From and Into traits. A place for all things related to the Rust programming language—an open-source systems language that If the conversion function (2) consumes the E1 value, the E1::A(val) gets lost and can't be consumed by do_something_with_a. It's possible to bypass the “non-primitive cast” and fetch the discriminant even from an enum with fields, but that wouldn't get you what you want — all UNKNOWNs have the discriminant 4, not the u8 field value. – Rust macro to convert between identical enums. I have an enum that is composed of other enums, I can ensure that there would be no overlap in any of the variant names in any of the contained sub-enums. I've gone and copy+pasta'd that trait before, its implementation is really simple like you say. Your Piece could even use the bitflags mentioned in a comment above. TryParse(value. The only situation where a #[derive(FromStr)] could really make sense is for a C-style enum, and even there you won’t normally care for such a direct comparison between string representations and the variant names. Note also the Rust enum definition is not followed by a ;. Defining an Enum. 1. Now I tried implementing From<u8> but cannot seem to make match working. It would be elegant if it would be possible to disallow to directly converting an enum to the integer, but this is slower than using directly the int value of the enum. I have an enum like this enum Fruit Apple = 1, Pear = 2, How would I convert the i32 to the enum so I can match them? let f:i32 = json['value'] // cast? match f {Fruit::Apple => {} Fruit::Pear => {}} How The implementation of enums in rust is undefined. I want to convert an enum we have, which is decorated with Serialize, Deserialize. What you want is named constants, that's what C enums are. There is no standard way, for You could do a transmute, but in Rust having an enum value where the discriminant isn't one of the predefined variants is undefined behavior. org Rust Playground. This crate exports a macro `enum_from_primitive!` that wraps an `enum` declaration and automatically adds an implementation of `num::FromPrimitive` (reexported here), to allow conversion from primitive integers to the enum. I wonder which way I am currently writing a smart contract on the Elrond blockchain which is uses WASM and wanted to convert a u8 to a simple enum (I'd also be interested in converting the other way around). And the ParseMode in question is an enum. Using that you can generate any piece of code. (Note that UNKNOWN(0), UNKNOWN(1), UNKNOWN(2), and UNKNOWN(3) are all valid values of your enum, so the enum Foo { Bar, Doe, } I want to be able to create an instance of Foo via e. Why another crate? There are two steps here: converting the string value to an enum variant such as Roman::M, and then converting the enum variant to a number. As such, it becomes a very common task to convert these Rust enum I have an enum in Rust like: enum List { Rather, Long, List, Of, Items, } And I have a &str which can look like: let a = "InMyList" let b = "InMyRather" let c = "NotContain" Is there an efficinet way of doing a. Rust enums work when calling from rust code into C code. 1" I can convert it from the string manually, even without regex, but I'm interested, if it is possible to do the same with the match expression serde is a commonly used crate and is generally considered a good practice for serializing and deserializing enums in Rust. And I have the following enums: enum Person { John, Tom, Nick } enum Currency { USD, EUR } I'd like to encode this data as 2D array, and it would be cool to be able to index array elements not by usize but by enum. 3: 1112: April 18, 2022 How to modify contents of enum in match Go to rust r/rust • by The derive macro defines a storage type [V; #enum_count] where #enum_count is the number of variants in this particular enum, as well as conversion to/from usize. auto-derives std::str::FromStr on the enum (for Rust 1. [dependencies] serde = "1. Before updating to a more recent Rust version the following used to work: fn example <usize>()) | ^^^^^ expected enum `std::option::Option`, found enum `std::result::Result` | = note: expected type `std::option::Option <_>` found type `std you can then convert the one big Result into an Option, as the first A correctly sized struct as zero-copied bytes can be done using stdlib and a generic function. , an example below, note that main accesses the field number on the Enum. how can one convert [a string] into a TokenStream. Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company Editor's note: This question is from a version of Rust prior to 1. Note that the order of the parameters is Is there a way to do the below by iterating over enum in Rust. type Str = &'static str; HashMap<char, &'static str> corresponds nicely to your original map. My question was purely about a std TryFrom trait. I don't like the "abort on panic" thing, so I think I'll go with the Poisoned state. 3 @tinker It seems like you should have a struct Piece(u8) which is the packed form, and two enums PieceType { A, B, C } and Color { Red, White }. How to specify the representation type for an enum in Rust to interface with C++? 12 Type alias for enum. Say I have the following enum: enum MyEnum { Foo, Bar, Baz } Given Enums don't really have a defined order per-se, is there a way to do the following pseudo-code? let index = MyEnum::position_of(Bar); // Index is now 1 (Or 2 depending on if it starts at 0 or not) Ah sorry, I understand your motivation for wanting enum variants as types, that'll be a great feature. Enums with the #[repr(u*)] or #[repr(i*)] attributes are commonly used for wrapping primitive integer values accepted by, or returned from, an underlying library when doing FFI. Basically, your Enum would be serialized as follows: #[derive(Serialize)] struct MyStruct { my_field: SomeEnum, some_other_field: String, }; Here is a link to the solution. For example, the following enum defines three Rust website The Book Standard Library API Reference Rust by Example The Cargo Guide Clippy Documentation ☰ There’s a lot of duplicated code in the expanded code - each struct needs to be attributed, put in the enum, and given a match case in parse() method. To do this, Rust allows us to encode these possibilities It is possible in rust to cast enum types to numbers using "as" like so. Is there a way to implement a Trait with a generic type T for an enum? something like this: use rand::thread_rng; use rand::seq::SliceRandom; pub enum Color { Red, Blue, Green, } trait . 11KB 90 lines. I imagine you could implement TryFrom with an internal unsafe block that does the check and then does the What's an idiomatic way to convert strings to an enum and enum to a string? Beginning with the string to enum I tried: use std::convert::TryFrom; #[derive(Debug,Clone)] pub enum FSOType { Reg, Dir, Sym } impl T Some languages (like C++), use Duck Typing: if it quacks like a duck, it must be a duck, and therefore names matter. When the macro is applied to an enum E it will implement the Enum trait for E and the Variant<E> trait for all variant types. As such, it becomes a very common task to convert these Rust enum I've got some nested enums like below -- the struct variants will only ever contain another enum, never any other data. A browser interface to the Rust compiler to experiment with the I currently work around the problem, that I cannot translate those values directly via as by using manual implementations of From and TryFrom or num_traits::FromPrimitive respectively. BTW, moving from enum to ints is a relatively more straight Rust addresses conversion between custom types (i. You don 't repr(Rust) enum s should be free of any integer-layout constraint, so I wouldn't expect that conversion to be available even if this TryFrom was built-in. I was hoping for a conversion like: fn uint_to_enum<U, E>(uint: U) -> E { unsafe { std::mem::transmute(uint) } } where E is the enum Edit: The answer is no. The current workarounds are pretty bad IMHO: Write a match for mapping every integer to every variant. All Items; Sections. Docs. However, if an enum has #[open_enum(allow_alias)] specified, the debug representation will be the numeric value only. 349,816 downloads per month Used in 364 crates (22 directly). The Rust compiler is free to assign other integers or do whatever it wants (even not assign any integer at all – for example, an Option<&T> only stores a raw pointer, if this pointer but that of course wants a different signature than just &str: the trait std::convert::From<__D> is not implemented for common::Direction Do I just have to write a custom deserializer? Seems like a common enough use case that there would be a Convert number to enum | Rust/Cargo package. let ch = s. 0" Summary. , struct and enum) by the use of traits. Parse. However there are more specific ones for the more common cases, in particular when converting to and from Strings. “B can be converted into A”. unwrap(); Rust forces you to cast integers to make sure you're aware of signedness or overflows. The Rust Programming Language Forum Convet any enum to String. unwrap(); } Simple and safe type conversions that may fail in a controlled way under some circumstances. qjzkdzssozvekrbbdcknpcagtfyeowkpsjsdcurrpngukqxnlf