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|
use std::any::TypeId;
use std::mem::{transmute_copy, ManuallyDrop};
use paste::paste;
use seq_macro::seq;
use util_macros::sub;
/// Used to append a element to a tuple type.
pub trait With<OtherElem>
{
type With;
}
/// Used to make all elements of a tuple type wrapped in [`Option`].
pub trait IntoInOptions
{
type InOptions: WithOptionElements;
fn into_in_options(self) -> Self::InOptions;
}
/// A tuple with all elements wrapped in [`Option`].
pub trait WithOptionElements
{
fn take<Element: 'static>(&mut self) -> TakeOptionElementResult<Element>;
}
/// Using the type system, reduces the elements of a tuple to a single one. Each element
/// determines itself how it is handled.
pub trait Reduce
{
type Out;
}
pub trait ReduceElement<Accumulator>
{
type Return;
}
/// The result of trying to [`take`] a element from a implementation of
/// [`WithOptionElements`].
///
/// [`take`]: WithOptionElements::take
pub enum TakeOptionElementResult<Element>
{
/// The element was succesfully taken.
Found(Element),
/// The element is not a element of the tuple.
NotFound,
/// The element has already been taken
AlreadyTaken,
}
/// Zero-sized struct implementing [`ReduceElement`] and just returns the accumulator.
#[derive(Debug, Clone, Copy)]
pub struct ReduceNoOp;
impl<Accumulator> ReduceElement<Accumulator> for ReduceNoOp
{
type Return = Accumulator;
}
macro_rules! tuple_reduce_elem_tuple {
(overflow) => {
()
};
($index: tt) => {
paste! {
[<Elem $index>]::Return
}
};
}
macro_rules! impl_tuple_traits {
($cnt: tt) => {
seq!(I in 0..$cnt {
impl<OtherElem, #(Elem~I,)*> With<OtherElem> for (#(Elem~I,)*) {
type With = (#(Elem~I,)* OtherElem,);
}
impl<#(Element~I: 'static,)*> IntoInOptions for (#(Element~I,)*)
{
type InOptions = (#(Option<Element~I>,)*);
fn into_in_options(self) -> Self::InOptions
{
#![allow(clippy::unused_unit)]
(#(Some(self.I),)*)
}
}
impl<#(Element~I: 'static,)*> WithOptionElements for (#(Option<Element~I>,)*)
{
fn take<Element: 'static>(&mut self)
-> TakeOptionElementResult<Element>
{
#(
if TypeId::of::<Element~I>() == TypeId::of::<Element>() {
let input = match self.I.take() {
Some(input) => ManuallyDrop::new(input),
None => {
return TakeOptionElementResult::AlreadyTaken;
}
};
return TakeOptionElementResult::Found(
// SAFETY: It can be transmuted safely since it is the
// same type and the type is 'static
unsafe { transmute_copy(&input) }
);
}
)*
TakeOptionElementResult::NotFound
}
}
paste! {
impl<#(Elem~I,)*> Reduce for (#(Elem~I,)*)
where
#(Elem~I: ReduceElement<sub!(I - 1, tuple_reduce_elem_tuple)>,)*
{
type Out = sub!($cnt - 1, tuple_reduce_elem_tuple);
}
}
});
};
}
seq!(N in 0..16 {
impl_tuple_traits!(N);
});
|
