Trait DiscreteFeature

pub trait DiscreteFeature<'a>: Sized {
    type Value: Parse<'a>;

    // Provided method
    fn parse_descrete_feature(
        p: &mut Parser<'a>,
        name: &'static str,
    ) -> Result<(LeftParen, Ident, Option<(Colon, Self::Value)>, RightParen)> { ... }
}

This trait provides an implementation for parsing a “Media Feature” that has a discrete keyword. This is complementary to the other media features: BooleanFeature and DiscreteFeature.

Rather than implementing this trait on an enum, use the discrete_feature! macro which expands to define the enum and necessary traits (Parse, this trait, and ToCursors) in a single macro call.

It does not implement Parse, but provides parse_discrere_feature(&mut Parser<'a>, name: &str) -> Result<Self>, which can make for a trivial Parse implementation. The name: &str parameter refers to the <feature-name> token, which will be parsed as an Ident. The DiscreteFeature::Value type must be implemented, and defines the <value> portion. Usually DiscreteFeature::Value can be easily defined using keyword_set!.

CSS defines the Media Feature generally as:

 │├─ "(" ─╮─ <feature-name> ─ ":" ─ <value> ─╭─ ")" ─┤│
          ├─ <feature-name> ─────────────────┤
          ╰─ <ranged-feature> ───────────────╯

The RangedFeature trait provides algorithms for parsing <ranged-feature> productions, but discrete features use the other two productions.

Given this, this trait parses as:

<feature-name>
 │├─ <ident> ─┤│

<discrete-feature>
 │├─ "(" ─╮─ <feature-name> ─ ":" ─ <value> ─╭─ ")" ─┤│
          ╰─ <feature-name> ─────────────────╯

Required Associated Types

type Value: Parse<'a>

Provided Methods

fn parse_descrete_feature( p: &mut Parser<'a>, name: &'static str, ) -> Result<(LeftParen, Ident, Option<(Colon, Self::Value)>, RightParen)>

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementors