Custom Attrs

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

Installation and Usage

Add this to your Cargo.toml file :

[dependencies]

custom_attrs = "1.5"

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,
}

Attribute properties

You can add properties to attributes to defines their characteristics. Even the documentation, in itself, is a property.

The syntax of a property is the following :

#[attr(
    #[<config_name> = <value>]
    <attribute>: <type>
)]

Configs can also be flags:

#[attr(
    #[<config_name>]
    <attribute>: <type>
)]

Like attributes, you can define many properties in one bloc:

#[attr(
    #[<config_name>, <config_name2> = <value>]
    <attribute>: <type>
])

Here is a list of all the properties :

function : defines the name of the function to get the attribute

Getting a value attribute

To get the value from a variant, simple call get_<attribute name> or the name /// you've set in the properties of the attributes.

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(
    #[function = "a_getter"]
    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
}

fn main() {
    Enum::Variant1.a_getter(); // custom getter name
    Enum::Variant2.get_b(); // default getter name
}

See the examples directory for more details.

Features

help_span : Merge main error and help notes, while these have they own span, and do not produce a separated error. This features is nightly only.

License

Licensed under the MIT license.

custom_attrs 1.5.3