enum-methods

Enum getter/is_* method generation.

Please note that this crate is unstable and is subject to change frequently.

I will attempt to prevent seriously breaking changes after we hit 0.1.0.

Usage

In your Cargo.toml, add this line under your [dependencies] section:

enum-methods = "0.0.5"

To use, simply derive and call methods (see the example below).

Why?

Usually when you write an enum with one or zero values, you might want to add a set of getters for them. As such:

#[derive(Debug)]
enum MyEnum {
    FooBarBaz(i64),
    BazBarFoo(String),
    // ... and others
}

impl MyEnum {
    pub fn foo_bar_baz(&self) -> i64 {
        if let &MyEnum::FooBarBaz(i) = self {
            i
        }
        else {
            panic!("called MyEnum::FooBarBaz() on {:?}", self)
        }
    }
    // et cetera
}

But this gets tedious, and adds a lot code for this simple functionality. Enter enum-methods.

Instead of doing the above with the if let ... else { panic!(...) }, you simply derive from the EnumIntoGetters

#[macro_use]
extern crate enum_methods;

#[derive(EnumIntoGetters, EnumAsGetters, EnumIsA, Debug)]
enum MyEnum {
    FooBarBaz(i64),
    // ... and others
}

fn main() {
    let my_foo = MyEnum::FooBarBaz(42);
    // EnumIsA - creates is_* methods for every member
    if my_foo.is_foo_bar_baz() {
        // EnumAsGetters - gets a reference to the enum, panicking if it is
        // not the specified variant
        assert_eq!(*my_foo.as_foo_bar_baz(), 42);
        // EnumIntoGetters - consumes the enum, yielding its owned value,
        // and panicking if it is not the specified variant
        assert_eq!(my_foo.into_foo_bar_baz(), 42);
    }
}

Requirements and gotchas

Right now, enum-methods has only three derivable options:

EnumAsGetters
EnumIntoGetters
EnumIsA

EnumAsGetters and EnumIntoGetters both have a couple of limitations.

Any enum variant which has exactly 1 member will have a getter generated for it. All other variants are ignored.
Enums which derive from EnumIntoGetters must also derive from Debug - this is for when a method is called for the wrong variant and needs to panic!.

EnumIsA is much simpler than the previous; it simply adds is_XXX methods returning a boolean for whether the variant matches or not.

For both methods, all names are automatically converted to snake_case.

License

This software is released under the Apache license 2.0. See the LICENSE file for more details.