[−][src]Crate strum
Strum
Strum is a set of macros and traits for working with enums and strings easier in Rust.
Including Strum in Your Project
Import strum and strum_macros into your project by adding the following lines to your Cargo.toml. Strum_macros contains the macros needed to derive all the traits in Strum.
[dependencies]
strum = "0.13.0"
strum_macros = "0.13.0"
And add these lines to the root of your project, either lib.rs or main.rs.
// Strum contains all the trait definitions extern crate strum; #[macro_use] extern crate strum_macros;
Strum Macros
Strum has implemented the following macros:
-
EnumString
: auto-derivesstd::str::FromStr
on the enum. Each variant of the enum will match on it's own name. This can be overridden usingserialize="DifferentName"
orto_string="DifferentName"
on the attribute as shown below. Multiple deserializations can be added to the same variant. If the variant contains additional data, they will be set to their default values upon deserialization.The
default
attribute can be applied to a tuple variant with a single data parameter. When a match isn't found, the given variant will be returned and the input string will be captured in the parameter.Here is an example of the code generated by deriving
EnumString
.#[derive(EnumString)] enum Color { Red, // The Default value will be inserted into range if we match "Green". Green { range:usize }, // We can match on multiple different patterns. #[strum(serialize="blue",serialize="b")] Blue(usize), // Notice that we can disable certain variants from being found #[strum(disabled="true")] Yellow, } /* //The generated code will look like: impl ::std::str::FromStr for Color { type Err = ::strum::ParseError; fn from_str(s: &str) -> ::std::result::Result<Color, Self::Err> { match s { "Red" => ::std::result::Result::Ok(Color::Red), "Green" => ::std::result::Result::Ok(Color::Green { range:Default::default() }), "blue" | "b" => ::std::result::Result::Ok(Color::Blue(Default::default())), _ => ::std::result::Result::Err(strum::ParseError::VariantNotFound), } } } */
Note that the implementation of
FromStr
by default only matches on the name of the variant. There is an option to match on different case conversions through the#[strum(serialize_all = "snake_case")]
type attribute. See the Additional Attributes Section for more information on using this feature. -
Display
,ToString
: both derives print out the given enum variant. This enables you to perform round trip style conversions from enum into string and back again for unit style variants.ToString
andDisplay
choose which serialization to used based on the following criteria:- If there is a
to_string
property, this value will be used. There can only be one per variant. - Of the various
serialize
properties, the value with the longest length is chosen. If that behavior isn't desired, you should useto_string
. - The name of the variant will be used if there are no
serialize
orto_string
attributes.
Display
should be preferred toToString
. All types that implement::std::fmt::Display
have a defaultToString
implementation.// You need to bring the type into scope to use it!!! use std::string::ToString; #[derive(Display, Debug)] enum Color { #[strum(serialize="redred")] Red, Green { range:usize }, Blue(usize), Yellow, } // It's simple to iterate over the variants of an enum. fn debug_colors() { let red = Color::Red; assert_eq!(String::from("redred"), red.to_string()); } fn main () { debug_colors(); }
- If there is a
-
AsRefStr
: this derive implementsAsRef<str>
on your enum using the same rules asToString
for determining what string is returned. The difference is thatas_ref()
returns a borrowedstr
instead of aString
so you can save an allocation. -
IntoStaticStr
: this trait implementsFrom<YourEnum>
andFrom<&'a YourEnum>
for&'static str
. This is useful for turning an enum variant into a static string. The Ruststd
provides a blanket impl of the reverse direction - i.e.impl Into<&'static str> for YourEnum
.
extern crate strum; #[macro_use] extern crate strum_macros; #[derive(IntoStaticStr)] enum State<'a> { Initial(&'a str), Finished } fn print_state<'a>(s:&'a str) { let state = State::Initial(s); // The following won't work because the lifetime is incorrect so we can use.as_static() instead. // let wrong: &'static str = state.as_ref(); let right: &'static str = state.into(); println!("{}", right); } fn main() { print_state(&"hello world".to_string()) }
-
EnumIter
: iterate over the variants of an Enum. Any additional data on your variants will be set toDefault::default()
. The macro implementsstrum::IntoEnumIter
on your enum and creates a new type calledYourEnumIter
that implements bothIterator
andExactSizeIterator
. You cannot deriveEnumIter
on any type with a lifetime bound (<'a>
) because the iterator would surely create [unbounded lifetimes] (https://doc.rust-lang.org/nightly/nomicon/unbounded-lifetimes.html).// You need to bring the type into scope to use it!!! use strum::IntoEnumIterator; #[derive(EnumIter,Debug)] enum Color { Red, Green { range:usize }, Blue(usize), Yellow, } // It's simple to iterate over the variants of an enum. fn debug_colors() { for color in Color::iter() { println!("My favorite color is {:?}", color); } } fn main() { debug_colors(); }
-
EnumMessage
: encode strings into the enum itself. This macro implements thestrum::EnumMessage
trait.EnumMessage
looks for#[strum(message="...")]
attributes on your variants. You can also provided adetailed_message="..."
attribute to create a seperate more detailed message than the first.The generated code will look something like:
// You need to bring the type into scope to use it!!! use strum::EnumMessage; #[derive(EnumMessage,Debug)] enum Color { #[strum(message="Red",detailed_message="This is very red")] Red, #[strum(message="Simply Green")] Green { range:usize }, #[strum(serialize="b",serialize="blue")] Blue(usize), } /* // Generated code impl ::strum::EnumMessage for Color { fn get_message(&self) -> ::std::option::Option<&str> { match self { &Color::Red => ::std::option::Option::Some("Red"), &Color::Green {..} => ::std::option::Option::Some("Simply Green"), _ => None } } fn get_detailed_message(&self) -> ::std::option::Option<&str> { match self { &Color::Red => ::std::option::Option::Some("This is very red"), &Color::Green {..}=> ::std::option::Option::Some("Simply Green"), _ => None } } fn get_serializations(&self) -> &[&str] { match self { &Color::Red => { static ARR: [&'static str; 1] = ["Red"]; &ARR }, &Color::Green {..}=> { static ARR: [&'static str; 1] = ["Green"]; &ARR }, &Color::Blue (..) => { static ARR: [&'static str; 2] = ["b", "blue"]; &ARR }, } } } */
-
EnumProperty
: Enables the encoding of arbitary constants into enum variants. This method currently only supports adding additional string values. Other types of literals are still experimental in the rustc compiler. The generated code works by nesting match statements. The first match statement matches on the type of the enum, and the inner match statement matches on the name of the property requested. This design works well for enums with a small number of variants and properties, but scales linearly with the number of variants so may not be the best choice in all situations.Here's an example:
// You need to bring the type into scope to use it!!! use strum::EnumProperty; #[derive(EnumProperty,Debug)] enum Color { #[strum(props(Red="255",Blue="255",Green="255"))] White, #[strum(props(Red="0",Blue="0",Green="0"))] Black, #[strum(props(Red="0",Blue="255",Green="0"))] Blue, #[strum(props(Red="255",Blue="0",Green="0"))] Red, #[strum(props(Red="0",Blue="0",Green="255"))] Green, } fn main() { let my_color = Color::Red; let display = format!("My color is {:?}. It's RGB is {},{},{}", my_color , my_color.get_str("Red").unwrap() , my_color.get_str("Green").unwrap() , my_color.get_str("Blue").unwrap()); }
-
EnumDiscriminants
: Given an enum namedMyEnum
, generates another enum calledMyEnumDiscriminants
with the same variants, without any data fields. This is useful when you wish to determine the variant of an enum from a String, but the variants contain any non-Default
fields. By default, the generated enum has the following derives:Clone, Copy, Debug, PartialEq, Eq
. You can add additional derives using the#[strum_discriminants(derive(AdditionalDerive))]
attribute.Here's an example:
// Bring trait into scope use std::str::FromStr; #[derive(Debug)] struct NonDefault; #[allow(dead_code)] #[derive(Debug, EnumDiscriminants)] #[strum_discriminants(derive(EnumString))] enum MyEnum { Variant0(NonDefault), Variant1 { a: NonDefault }, } fn main() { assert_eq!( MyEnumDiscriminants::Variant0, MyEnumDiscriminants::from_str("Variant0").unwrap() ); }
You can also rename the generated enum using the
#[strum_discriminants(name(OtherName))]
attribute:// You need to bring the type into scope to use it!!! use strum::IntoEnumIterator; #[allow(dead_code)] #[derive(Debug, EnumDiscriminants)] #[strum_discriminants(name(MyVariants), derive(EnumIter))] enum MyEnum { Variant0(bool), Variant1 { a: bool }, } fn main() { assert_eq!( vec![MyVariants::Variant0, MyVariants::Variant1], MyVariants::iter().collect::<Vec<_>>() ); }
The derived enum also has the following trait implementations:
impl From<MyEnum> for MyEnumDiscriminants
impl<'_enum> From<&'_enum MyEnum> for MyEnumDiscriminants
These allow you to get the Discriminants enum variant from the original enum:
extern crate strum; #[macro_use] extern crate strum_macros; #[derive(Debug, EnumDiscriminants)] #[strum_discriminants(name(MyVariants))] enum MyEnum { Variant0(bool), Variant1 { a: bool }, } fn main() { assert_eq!(MyVariants::Variant0, MyEnum::Variant0(true).into()); }
-
EnumCount
: for a given enum generates implementation ofstrum::EnumCount
, which returns number of variants viastrum::EnumCount::count
method, also for givenenum MyEnum
generatesconst MYENUM_COUNT: usize
which gives the same value asstrum::EnumCount
(which is usefull for array sizes, etc.).extern crate strum; #[macro_use] extern crate strum_macros; use strum::{IntoEnumIterator, EnumCount}; #[derive(Debug, EnumCount, EnumIter)] enum Week { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, } fn main() { assert_eq!(7, Week::count()); assert_eq!(Week::count(), WEEK_COUNT); assert_eq!(Week::iter().count(), WEEK_COUNT); }
Additional Attributes
Strum supports several custom attributes to modify the generated code. At the enum level, the
#[strum(serialize_all = "snake_case")]
attribute can be used to change the case used when
serializing to and deserializing from strings:
extern crate strum; #[macro_use] extern crate strum_macros; #[derive(Debug, Eq, PartialEq, ToString)] #[strum(serialize_all = "snake_case")] enum Brightness { DarkBlack, Dim { glow: usize, }, #[strum(serialize = "bright")] BrightWhite, } fn main() { assert_eq!( String::from("dark_black"), Brightness::DarkBlack.to_string().as_ref() ); assert_eq!( String::from("dim"), Brightness::Dim { glow: 0 }.to_string().as_ref() ); assert_eq!( String::from("bright"), Brightness::BrightWhite.to_string().as_ref() ); }
Custom attributes are applied to a variant by adding #[strum(parameter="value")]
to the variant.
-
serialize="..."
: Changes the text thatFromStr()
looks for when parsing a string. This attribute can be applied multiple times to an element and the enum variant will be parsed if any of them match. -
default="true"
: Applied to a single variant of an enum. The variant must be a Tuple-like variant with a single piece of data that can be create from a&str
i.e.T: From<&str>
. The generated code will now return the variant with the input string captured as shown below instead of failing.ⓘThis example is not tested// Replaces this: _ => Err(strum::ParseError::VariantNotFound) // With this in generated code: default => Ok(Variant(default.into()))
The plugin will fail if the data doesn't implement From<&str>. You can only have one
default
on your enum. -
disabled="true"
: removes variant from generated code. -
message=".."
: Adds a message to enum variant. This is used in conjunction with theEnumMessage
trait to associate a message with a variant. Ifdetailed_message
is not provided, thenmessage
will also be returned when get_detailed_message() is called. -
detailed_message=".."
: Adds a more detailed message to a variant. If this value is omitted, thenmessage
will be used in it's place. -
props(key="value")
: Used by EnumProperty to add additional information to an enum variant. Multiple properties can be added in a single nested block.
Examples
Using EnumMessage
for quickly implementing Error
extern crate strum; #[macro_use] extern crate strum_macros; use strum::EnumMessage; #[derive(Debug, EnumMessage)] enum ServerError { #[strum(message="A network error occured")] #[strum(detailed_message="Try checking your connection.")] NetworkError, #[strum(message="User input error.")] #[strum(detailed_message="There was an error parsing user input. Please try again.")] InvalidUserInputError, } impl Display for ServerError { fn fmt(&self, f: &mut Formatter) -> Result { write!(f, "{}", self.get_message().unwrap()) } } impl Error for ServerError { fn description(&self) -> &str { self.get_detailed_message().unwrap() } }
Using EnumString
to tokenize a series of inputs:
extern crate strum; #[macro_use] extern crate strum_macros; use std::str::FromStr; #[derive(Eq, PartialEq, Debug, EnumString)] enum Tokens { #[strum(serialize="fn")] Function, #[strum(serialize="(")] OpenParen, #[strum(serialize=")")] CloseParen, #[strum(default="true")] Ident(String) } fn main() { let toks = ["fn", "hello_world", "(", ")"].iter() .map(|tok| Tokens::from_str(tok).unwrap()) .collect::<Vec<_>>(); assert_eq!(toks, vec![Tokens::Function, Tokens::Ident(String::from("hello_world")), Tokens::OpenParen, Tokens::CloseParen]); }
Debugging
To see the generated code, set the STRUM_DEBUG environment variable before compiling your code.
STRUM_DEBUG=1
will dump all of the generated code for every type. STRUM_DEBUG=YourType
will
only dump the code generated on a type named YourType.
Enums
ParseError | The ParseError enum is a collection of all the possible reasons an enum can fail to parse from a string. |
Traits
AsStaticRef | A cheap reference-to-reference conversion. Used to convert a value to a
reference value with |
EnumCount | A trait for capturing the number of variants in Enum. This trait can be autoderived by
|
EnumMessage | Associates additional pieces of information with an Enum. This can be
autoimplemented by deriving |
EnumProperty | EnumProperty is a trait that makes it possible to store additional information
with enum variants. This trait is designed to be used with the macro of the same
name in the |
IntoEnumIterator | This trait designates that an |