1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
|
#![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 0, $iter:expr, ($body:expr), $x:ident.., $($rest:tt)*) => {
$crate::destructure_iter!(@match 1, $iter, ({
let $x = $iter;
$body
}), $($rest)*)
};
// Variable length pattern without a binder
(@match 0, $iter:expr, ($body:expr), .., $($rest:tt)*) => {
$crate::destructure_iter!(@match 1, $iter, ($body), $($rest)*)
};
// Single item pattern
(@match 0, $iter:expr, ($body:expr), $x:pat, $($rest:tt)*) => {
if let Some($x) = $iter.next() {
$crate::destructure_iter!(@match 0, $iter, ($body), $($rest)*)
} else {
None
}
};
// Single item pattern after a variable length one: declare reversed and take from the end
(@match 1, $iter:expr, ($body:expr), $x:pat, $($rest:tt)*) => {
$crate::destructure_iter!(@match 1, $iter, (
if let Some($x) = $iter.next_back() {
$body
} else {
None
}
), $($rest)*)
};
// Check no elements remain
(@match 0, $iter:expr, ($body:expr) $(,)*) => {
if $iter.next().is_some() {
None
} else {
$body
}
};
// After a variable length pattern, everything has already been consumed
(@match 1, $iter:expr, ($body:expr) $(,)*) => {
$body
};
($iter:expr; [$($args:tt)*] => $body:expr) => {
{
#[allow(unused_mut)]
let mut iter = $iter;
$crate::destructure_iter!(@match 0, iter, (Some($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();
}
|
