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use core::{any::TypeId, convert, marker::PhantomData};
/// Specialized behavior runner (Owned -> Owned)
#[derive(Debug)]
pub struct Specializer<T, U, F>(T, F, PhantomData<fn(T) -> U>);
impl<T, U, F> Specializer<T, U, F>
where
F: FnOnce(T) -> U,
T: 'static,
U: 'static,
{
/// Create a new specializer with a fallback function.
#[inline(always)]
pub const fn new(params: T, f: F) -> Self {
Self(params, f, PhantomData)
}
/// Specialize on the parameter and the return type of the closure.
///
/// ```rust
/// use specializer::Specializer;
///
/// fn specialized<T, U>(ty: T) -> U
/// where
/// T: 'static,
/// U: 'static + From<T> + From<u8>,
/// {
/// Specializer::new(ty, From::from)
/// .specialize(|int: i32| -> i32 { int * 2 })
/// .specialize_param(|int: u8| { U::from(int * 3) })
/// .run()
/// }
///
/// assert_eq!(specialized::<i16, i32>(3), 3);
/// assert_eq!(specialized::<i32, i32>(3), 6);
/// assert_eq!(specialized::<u8, i32>(3), 9);
/// ```
#[inline]
pub fn specialize<P, R>(
self,
f: impl FnOnce(P) -> R,
) -> Specializer<T, U, impl FnOnce(T) -> U>
where
P: 'static,
R: 'static,
{
let Specializer(ty, fallback, phantom_data) = self;
let f = |t: T| -> U {
if TypeId::of::<T>() == TypeId::of::<P>()
&& TypeId::of::<U>() == TypeId::of::<R>()
{
let param = crate::cast_identity::<T, P>(t).unwrap();
return crate::cast_identity::<R, U>(f(param)).unwrap();
}
fallback(t)
};
Specializer(ty, f, phantom_data)
}
/// Specialize on the parameter and the return type of the closure, mapping
/// both.
///
/// ```rust
/// use std::convert;
///
/// use specializer::Specializer;
///
/// fn specialized<T, U>(ty: T) -> U
/// where
/// T: 'static,
/// U: 'static + From<T>,
/// {
/// Specializer::new(ty, From::from)
/// .specialize(|int: i32| -> i32 { int * 2 })
/// .specialize_map(
/// |int: u8| int * 3,
/// From::from,
/// convert::identity::<U>,
/// )
/// .run()
/// }
///
/// assert_eq!(specialized::<i16, i32>(3), 3);
/// assert_eq!(specialized::<i32, i32>(3), 6);
/// assert_eq!(specialized::<u8, i32>(3), 9);
/// ```
#[inline]
pub fn specialize_map<P, R>(
self,
p: impl FnOnce(P) -> P,
f: impl FnOnce(T) -> U,
r: impl FnOnce(R) -> R,
) -> Specializer<T, U, impl FnOnce(T) -> U>
where
P: 'static,
R: 'static,
{
let Specializer(ty, fallback, phantom_data) = self;
let f = |t: T| -> U {
if TypeId::of::<T>() == TypeId::of::<P>()
&& TypeId::of::<U>() == TypeId::of::<R>()
{
let param = crate::cast_identity::<T, P>(t).unwrap();
let param = crate::cast_identity::<P, T>(p(param)).unwrap();
let ret = crate::cast_identity::<U, R>(f(param)).unwrap();
return crate::cast_identity::<R, U>(r(ret)).unwrap();
}
fallback(t)
};
Specializer(ty, f, phantom_data)
}
/// Specialize on the parameter of the closure.
///
/// ```rust
/// use specializer::Specializer;
///
/// fn specialized<T>(ty: T) -> String
/// where
/// T: 'static
/// {
/// let fallback = |_| "unknown".to_owned();
///
/// Specializer::new(ty, fallback)
/// .specialize_param(|int: i32| (int * 2).to_string())
/// .specialize_param(|string: String| string)
/// .run()
/// }
///
/// assert_eq!(specialized(3), "6");
/// assert_eq!(specialized("Hello world".to_string()), "Hello world");
/// assert_eq!(specialized(()), "unknown");
/// ```
#[inline]
pub fn specialize_param<P>(
self,
f: impl FnOnce(P) -> U,
) -> Specializer<T, U, impl FnOnce(T) -> U>
where
P: 'static,
{
self.specialize::<P, U>(f)
}
/// Specialize on the return type of the closure.
///
/// ```rust
/// use specializer::Specializer;
///
/// fn specialized<T>(int: i32) -> T
/// where
/// T: 'static + Default
/// {
/// let fallback = |_| -> T { Default::default() };
///
/// Specializer::new(int, fallback)
/// .specialize_return(|int| -> i32 { int * 2 })
/// .specialize_return(|int| -> String { int.to_string() })
/// .run()
/// }
///
/// assert_eq!(specialized::<i32>(3), 6);
/// assert_eq!(specialized::<String>(3), "3");
/// assert_eq!(specialized::<u8>(3), 0);
/// ```
#[inline]
pub fn specialize_return<R>(
self,
f: impl FnOnce(T) -> R,
) -> Specializer<T, U, impl FnOnce(T) -> U>
where
R: 'static,
{
self.specialize::<T, R>(f)
}
/// Specialize on the parameter and the return type of the closure, mapping
/// the parameter.
///
/// ```rust
/// use std::convert;
///
/// use specializer::Specializer;
///
/// fn specialized<T, U>(ty: T) -> U
/// where
/// T: 'static,
/// U: 'static + From<T>,
/// {
/// Specializer::new(ty, From::from)
/// .specialize(|int: i32| -> i32 { int * 2 })
/// .specialize_map_param(|int: u8| int * 3, From::from)
/// .run()
/// }
///
/// assert_eq!(specialized::<i16, i32>(3), 3);
/// assert_eq!(specialized::<i32, i32>(3), 6);
/// assert_eq!(specialized::<u8, i32>(3), 9);
/// ```
#[inline]
pub fn specialize_map_param<P>(
self,
p: impl FnOnce(P) -> P,
f: impl FnOnce(T) -> U,
) -> Specializer<T, U, impl FnOnce(T) -> U>
where
P: 'static,
{
self.specialize_map::<P, U>(p, f, convert::identity)
}
/// Specialize on the parameter and the return type of the closure, mapping
/// the parameter.
///
/// ```rust
/// use std::convert;
///
/// use specializer::Specializer;
///
/// fn specialized<T, U>(ty: T) -> U
/// where
/// T: 'static,
/// U: 'static + From<T>,
/// {
/// Specializer::new(ty, From::from)
/// .specialize_map_return(From::from, |int: i16| int * 2)
/// .specialize_map_param(|int: u8| int * 3, From::from)
/// .run()
/// }
///
/// assert_eq!(specialized::<i16, i32>(3), 3);
/// assert_eq!(specialized::<i8, i16>(3), 6);
/// assert_eq!(specialized::<u8, i32>(3), 9);
/// ```
#[inline]
pub fn specialize_map_return<R>(
self,
f: impl FnOnce(T) -> U,
r: impl FnOnce(R) -> R,
) -> Specializer<T, U, impl FnOnce(T) -> U>
where
R: 'static,
{
self.specialize_map::<T, R>(convert::identity, f, r)
}
/// Run the specializer.
#[inline]
pub fn run(self) -> U {
(self.1)(self.0)
}
}