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|
#![feature(slice_patterns)]
/* Destructure an iterator using the syntax of slice_patterns.
* Wraps the match body in `Some` if there was a match; returns
* `None` otherwise.
* Contrary to slice_patterns, this allows moving out
* of the iterator.
* A variable length pattern (`x..`) is only allowed as the last
* pattern, unless the iterator is double-ended.
*
* Example:
* ```
* let vec = vec![Some(1), Some(2), None];
*
* destructure_iter!(vec.into_iter();
* [Some(x), y.., z] => {
* // x: usize
* // y: impl Iterator<Option<usize>>
* // z: Option<usize>
* }
* )
* ```
*
*/
#[macro_export]
macro_rules! destructure_iter {
// Variable length pattern
(@match_forwards, $iter:expr, ($body:expr), $x:ident.., $($rest:tt)*) => {
$crate::destructure_iter!(@match_backwards, $iter, ({
let $x = $iter;
$body
}), $($rest)*)
};
// Variable length pattern without a binder
(@match_forwards, $iter:expr, ($body:expr), .., $($rest:tt)*) => {
$crate::destructure_iter!(@match_backwards, $iter, ($body), $($rest)*)
};
// Single item pattern
(@match_forwards, $iter:expr, ($body:expr), $x:pat, $($rest:tt)*) => {
if let Some($x) = $iter.next() {
$crate::destructure_iter!(@match_forwards, $iter, ($body), $($rest)*)
} else {
None
}
};
// Single item pattern after a variable length one: declare reversed and take from the end
(@match_backwards, $iter:expr, ($body:expr), $x:pat, $($rest:tt)*) => {
$crate::destructure_iter!(@match_backwards, $iter, (
if let Some($x) = $iter.next_back() {
$body
} else {
None
}
), $($rest)*)
};
// Check no elements remain
(@match_forwards, $iter:expr, ($body:expr) $(,)*) => {
if $iter.next().is_some() {
None
} else {
$body
}
};
// After a variable length pattern, everything has already been consumed
(@match_backwards, $iter:expr, ($body:expr) $(,)*) => {
$body
};
($iter:expr; [$($args:tt)*] => $body:expr) => {
{
#[allow(unused_mut)]
let mut iter = $iter;
$crate::destructure_iter!(@match_forwards, iter, (Some($body)), $($args)*,)
}
};
}
/* Pattern-match on a vec using the syntax of slice_patterns.
* Wraps the match body in `Some` if there was a match; returns
* `None` otherwise.
* A variable length pattern (`x..`) returns an iterator.
*
* Example:
* ```
* let vec = vec![Some(1), Some(2), None];
*
* match_vec!(vec;
* [Some(x), y.., z] => {
* // x: usize
* // y: impl Iterator<Option<usize>>
* // z: Option<usize>
* }
* [x, Some(0)] => {
* // x: Option<usize>
* },
* [..] => { }
* )
* ```
*
*/
#[macro_export]
macro_rules! match_vec {
($arg:expr; $( [$($args:tt)*] => $body:expr ),* $(,)*) => {
{
let vec = $arg;
// Match as references to decide which branch to take
// I think `match_default_bindings` should make this always work but
// there may be some patterns this doesn't capture.
#[allow(unused_variables, unreachable_patterns)]
match vec.as_slice() {
$(
[$($args)*] => {
// Actually consume the values
#[allow(unused_mut)]
let mut iter = vec.into_iter();
$crate::destructure_iter!(iter; [$($args)*] => $body)
}
)*
_ => None,
}
}
};
}
/* Pattern-match on an iterator using the syntax of slice_patterns.
* Wraps the match body in `Some` if there was a match; returns
* `None` otherwise.
*
* Example:
* ```
* let vec = vec![Some(1), Some(2), None];
*
* match_iter!(vec.into_iter();
* [Some(x), y.., z] => {
* // x: usize
* // y: impl Iterator<Option<usize>>
* // z: Option<usize>
* },
* [x, Some(0)] => {
* // x: Option<usize>
* },
* [..] => {
* )
* ```
*
*/
#[macro_export]
macro_rules! match_iter {
($arg:expr; $($args:tt)*) => {
{
let vec: Vec<_> = $arg.collect();
$crate::match_vec!(vec; $($args)*)
}
};
}
#[test]
fn test() {
let test = |v: Vec<Option<isize>>| {
match_vec!(v.into_iter();
[Some(_x), None, None] => 4,
[Some(_x), None] => 2,
[None, Some(y)] => 1,
[None, _y..] => 3,
[_x.., Some(y), Some(z)] => y - z,
[] => 0,
[..] => -1,
)
.unwrap()
};
assert_eq!(test(vec![Some(0), None, None]), 4);
assert_eq!(test(vec![Some(0), None]), 2);
assert_eq!(test(vec![None, Some(0)]), 1);
assert_eq!(test(vec![Some(1), Some(2), Some(5), Some(14)]), -9);
assert_eq!(test(vec![None]), 3);
assert_eq!(test(vec![]), 0);
assert_eq!(test(vec![Some(0)]), -1);
// Test move out of pattern
struct Foo;
let _: (Foo, Foo) = match_vec!(vec![Some(Foo), Some(Foo)].into_iter();
[Some(f1), Some(f2)] => (f1, f2),
)
.unwrap();
}
|
