Custom Attrs

A library that allows you to configure values specific to each variants of an enum.

Installation and Usage

Add this to your Cargo.toml file :

[dependencies]

custom_attrs = "1.4"

Then you can use the derive attribute to use the library.

use custom_attrs::CustomAttrs;

#[derive(CustomAttrs)]

// all attributes declarations will be here.

enum Enum {
    // ...
}

Attribute declaration.

By default, an attribute declaration is composed of two parts : an attribute's name and it's type.

#[attr(name: u32)]
enum Enum {}

You can declare many attribute declarations in a single attr.

#[attr(
    name: u32,
    name2: usize
)]
enum Enum {}

Optionally, you can add more components.

Optional components

You can set the visibility of the attribute. This will change the visibility of the getter function.

#[attr(pub name: u32)]
enum Enum {}

By default, each attribute declared require a value to be set for each variant. If this requirement is not set, the library will produce an error.

You can disable this behavior by making it optional, by writing type into an Option, or by adding a default value behind the attribute declaration. See the example below.

#[attr(name: Option<u32>)]
enum Enum {}

#[attr(name: u32 = 3)]
enum Enum {}

You can add documentation avoid declared attributes. This documentation will override the one of the getter function.

#[attr(
    /// Attribute documentation
    attribute: u32
)]
enum Enum {}

Setting a value

To set a value for a variant, just add the name of the attribute followed by the value you want to set.

enum Enum {
    #[attr(name = 4)]
    VariantA
}

Like declarations, you can set many values at once.

enum Enum {
    #[attr(
        name = 4,
        name2 = 1
    )]
    VariantA
}

If the attribute is optional, you don't have to wrap it in a Some. custom_attrs will do this for you. If you want the value to be None, just put None behind the it.

enum Enum {
    #[attr(name = 4)]
    VariantA,

    #[attr(name = None)]
    VariantB,

    // you can still wrap the value into an option
    #[attr(name = Some(5))]
    VariantC,
}

Getting a value attribute

To get the value from a variant, simple call get_<attribute name>.

Element::VariantA.get_a();

If you've set a documentation on the attribute, it will be shown on this function.

Examples

use custom_attrs::CustomAttrs;

// ...

#[derive(CustomAttrs)]

#[attr(pub a: usize)]
#[attr(b: Option<usize>)]
#[attr(c: &'static str = "Hello world!")]
enum Enum {
    #[attr(a = 5)]
    #[attr(b = 3)]
    Variant1,

    #[attr(a = 3)]
    #[attr(c = "Hello again !")]
    Variant2,

    #[attr(
        a = 1,
        b = 5,
        c = "Hello for the last time !"
    )]
    Variant3
}

See the examples directory for more details.

License

Licensed under the MIT license.

custom_attrs 1.4.0