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#![no_std] //! This crate allows for the creation //! of type-level values. Any value can //! be type-level as long as it can be //! initialized as a constant. All //! type-level values implement the //! TypeVal trait, and so can be provided //! as type parameters. /// A trait implemented by type-level /// values. pub trait TypeVal<T> { /// The value held. const VAL: T; } /// This macro is used to implement the /// TypeVal trait. Any number of values /// can be initialized with a single /// invocation, but every value in a /// single invocation must be either /// public or private. Attributes to /// be applied to items in a block, /// including doc comments, should go /// above their targets. /// /// ## Example /// /// ```rust /// // Private /// def_type_val! { /// type One: i32 = 1; /// #[derive(Clone, Copy)] /// type True: bool = true; /// } /// /// // Public /// def_type_val! { /// /// Negative one /// pub type NegOne: i32 = -1; /// pub type False: bool = false; /// } /// ``` #[macro_export] macro_rules! def_type_val { {$($(#[$attr:meta])* type $name:ident: $type:ident = $value:expr;)+} => { $( $(#[$attr])* struct $name; impl $crate::TypeVal<$type> for $name { const VAL: $type = $value; } )+ }; {$($(#[$attr:meta])* pub type $name:ident: $type:ident = $value:expr;)+} => { $( $(#[$attr])* pub struct $name; impl $crate::TypeVal<$type> for $name { const VAL: $type = $value; } )+ }; }