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86650211
编写于
2月 03, 2016
作者:
M
Manish Goregaokar
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Rollup merge of #31352 - steveklabnik:gh31154, r=nikomatsakis
Fixes #31154
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5540605c
6c907212
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src/doc/book/patterns.md
src/doc/book/patterns.md
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src/doc/book/patterns.md
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86650211
...
...
@@ -173,7 +173,39 @@ let (x, _, z) = coordinate();
Here, we bind the first and last element of the tuple to
`x`
and
`z`
, but
ignore the middle element.
Similarly, you can use
`..`
in a pattern to disregard multiple values.
It’s worth noting that using
`_`
never binds the value in the first place,
which means a value may not move:
```
rust
let
tuple
:
(
u32
,
String
)
=
(
5
,
String
::
from
(
"five"
));
// Here, tuple is moved, because the String moved:
let
(
x
,
_
s
)
=
tuple
;
// The next line would give "error: use of partially moved value: `tuple`"
// println!("Tuple is: {:?}", tuple);
// However,
let
tuple
=
(
5
,
String
::
from
(
"five"
));
// Here, tuple is _not_ moved, as the String was never moved, and u32 is Copy:
let
(
x
,
_
)
=
tuple
;
// That means this works:
println!
(
"Tuple is: {:?}"
,
tuple
);
```
This also means that any temporary variables will be dropped at the end of the
statement:
```
rust
// Here, the String created will be dropped immediately, as it’s not bound:
let
_
=
String
::
from
(
" hello "
)
.trim
();
```
You can also use
`..`
in a pattern to disregard multiple values:
```
rust
enum
OptionalTuple
{
...
...
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