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//! All of the **marker traits** used in typenum.
//!
//! Note that the definition here for marker traits is slightly different than
//! the conventional one -- we include traits with functions that convert a type
//! to the corresponding value, as well as associated constants that do the
//! same.
//!
//! For example, the `Integer` trait includes the function (among others) `fn
//! to_i32() -> i32` and the associated constant `I32` so that one can do this:
//!
//! ```
//! use typenum::{Integer, N42};
//!
//! assert_eq!(-42, N42::to_i32());
//! assert_eq!(-42, N42::I32);
//! ```

use crate::sealed::Sealed;

/// A **marker trait** to designate that a type is not zero. All number types in this
/// crate implement `NonZero` except `B0`, `U0`, and `Z0`.
pub trait NonZero: Sealed {}

/// A **marker trait** to designate that a type is zero. Only `B0`, `U0`, and `Z0`
/// implement this trait.
pub trait Zero: Sealed {}

/// A **Marker trait** for the types `Greater`, `Equal`, and `Less`.
pub trait Ord: Sealed {
    #[allow(missing_docs)]
    fn to_ordering() -> ::core::cmp::Ordering;
}

/// The **marker trait** for compile time bits.
pub trait Bit: Sealed + Copy + Default + 'static {
    #[allow(missing_docs)]
    const U8: u8;
    #[allow(missing_docs)]
    const BOOL: bool;

    /// Instantiates a singleton representing this bit.
    fn new() -> Self;

    #[allow(missing_docs)]
    fn to_u8() -> u8;
    #[allow(missing_docs)]
    fn to_bool() -> bool;
}

/// The **marker trait** for compile time unsigned integers.
///
/// # Example
/// ```rust
/// use typenum::{Unsigned, U3};
///
/// assert_eq!(U3::to_u32(), 3);
/// assert_eq!(U3::I32, 3);
/// ```
pub trait Unsigned: Sealed + Copy + Default + 'static {
    #[allow(missing_docs)]
    const U8: u8;
    #[allow(missing_docs)]
    const U16: u16;
    #[allow(missing_docs)]
    const U32: u32;
    #[allow(missing_docs)]
    const U64: u64;
    #[cfg(feature = "i128")]
    #[allow(missing_docs)]
    const U128: u128;
    #[allow(missing_docs)]
    const USIZE: usize;

    #[allow(missing_docs)]
    const I8: i8;
    #[allow(missing_docs)]
    const I16: i16;
    #[allow(missing_docs)]
    const I32: i32;
    #[allow(missing_docs)]
    const I64: i64;
    #[cfg(feature = "i128")]
    #[allow(missing_docs)]
    const I128: i128;
    #[allow(missing_docs)]
    const ISIZE: isize;

    #[allow(missing_docs)]
    fn to_u8() -> u8;
    #[allow(missing_docs)]
    fn to_u16() -> u16;
    #[allow(missing_docs)]
    fn to_u32() -> u32;
    #[allow(missing_docs)]
    fn to_u64() -> u64;
    #[cfg(feature = "i128")]
    #[allow(missing_docs)]
    fn to_u128() -> u128;
    #[allow(missing_docs)]
    fn to_usize() -> usize;

    #[allow(missing_docs)]
    fn to_i8() -> i8;
    #[allow(missing_docs)]
    fn to_i16() -> i16;
    #[allow(missing_docs)]
    fn to_i32() -> i32;
    #[allow(missing_docs)]
    fn to_i64() -> i64;
    #[cfg(feature = "i128")]
    #[allow(missing_docs)]
    fn to_i128() -> i128;
    #[allow(missing_docs)]
    fn to_isize() -> isize;
}

/// The **marker trait** for compile time signed integers.
///
/// # Example
/// ```rust
/// use typenum::{Integer, P3};
///
/// assert_eq!(P3::to_i32(), 3);
/// assert_eq!(P3::I32, 3);
/// ```
pub trait Integer: Sealed + Copy + Default + 'static {
    #[allow(missing_docs)]
    const I8: i8;
    #[allow(missing_docs)]
    const I16: i16;
    #[allow(missing_docs)]
    const I32: i32;
    #[allow(missing_docs)]
    const I64: i64;
    #[cfg(feature = "i128")]
    #[allow(missing_docs)]
    const I128: i128;
    #[allow(missing_docs)]
    const ISIZE: isize;

    #[allow(missing_docs)]
    fn to_i8() -> i8;
    #[allow(missing_docs)]
    fn to_i16() -> i16;
    #[allow(missing_docs)]
    fn to_i32() -> i32;
    #[allow(missing_docs)]
    fn to_i64() -> i64;
    #[cfg(feature = "i128")]
    #[allow(missing_docs)]
    fn to_i128() -> i128;
    #[allow(missing_docs)]
    fn to_isize() -> isize;
}

/// The **marker trait** for type-level arrays of type-level numbers.
///
/// Someday, it may contain an associated constant to produce a runtime array,
/// like the other marker traits here. However, that is blocked by [this
/// issue](https://github.com/rust-lang/rust/issues/44168).
pub trait TypeArray: Sealed {}

/// The **marker trait** for type-level numbers which are a power of two.
///
/// # Examples
///
/// Here's a working example:
///
/// ```rust
/// use typenum::{PowerOfTwo, P4, P8};
///
/// fn only_p2<P: PowerOfTwo>() {}
///
/// only_p2::<P4>();
/// only_p2::<P8>();
/// ```
///
/// Numbers which are not a power of two will fail to compile in this example:
///
/// ```rust,compile_fail
/// use typenum::{P9, P511, P1023, PowerOfTwo};
///
/// fn only_p2<P: PowerOfTwo>() { }
///
/// only_p2::<P9>();
/// only_p2::<P511>();
/// only_p2::<P1023>();
/// ```
pub trait PowerOfTwo: Sealed {}