Borrowed value does not live long enough when iterating over a generic value with a lifetime on the function...
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fn func<'a, T>(arg: Vec<Box<T>>)
where
String: From<&'a T>,
T: 'a,
{
let s: Vec<String> = arg.iter().map(|s| String::from(s)).collect();
do_something_else(arg);
}
fn do_something_else<T>(arg: Vec<Box<T>>) {}
The compiler complains that arg does not live long enough. Why though?
error[E0597]: `arg` does not live long enough
--> src/lib.rs:6:26
|
6 | let s: Vec<String> = arg.iter().map(|s| String::from(s)).collect();
| ^^^ borrowed value does not live long enough
7 | do_something_else(arg);
8 | }
| - borrowed value only lives until here
|
note: borrowed value must be valid for the lifetime 'a as defined on the function body at 1:9...
--> src/lib.rs:1:9
|
1 | fn func<'a, T>(arg: Vec<Box<T>>)
| ^^
rust lifetime
edited Nov 26 '18 at 17:13
Shepmaster
161k16330474
asked Nov 26 '18 at 16:45
NirmanNirman
534
add a comment |
fn func<'a, T>(arg: Vec<Box<T>>)
where
String: From<&'a T>,
T: 'a,
{
let s: Vec<String> = arg.iter().map(|s| String::from(s)).collect();
do_something_else(arg);
}
fn do_something_else<T>(arg: Vec<Box<T>>) {}
The compiler complains that arg does not live long enough. Why though?
error[E0597]: `arg` does not live long enough
--> src/lib.rs:6:26
|
6 | let s: Vec<String> = arg.iter().map(|s| String::from(s)).collect();
| ^^^ borrowed value does not live long enough
7 | do_something_else(arg);
8 | }
| - borrowed value only lives until here
|
note: borrowed value must be valid for the lifetime 'a as defined on the function body at 1:9...
--> src/lib.rs:1:9
|
1 | fn func<'a, T>(arg: Vec<Box<T>>)
| ^^
rust lifetime
edited Nov 26 '18 at 17:13
Shepmaster
161k16330474
asked Nov 26 '18 at 16:45
NirmanNirman
534
So you want to useargafter collecting the members intos? Else I would say useinto_iterand it's all done.
– hellow
Nov 26 '18 at 16:58
add a comment |
fn func<'a, T>(arg: Vec<Box<T>>)
where
String: From<&'a T>,
T: 'a,
{
let s: Vec<String> = arg.iter().map(|s| String::from(s)).collect();
do_something_else(arg);
}
fn do_something_else<T>(arg: Vec<Box<T>>) {}
The compiler complains that arg does not live long enough. Why though?
error[E0597]: `arg` does not live long enough
--> src/lib.rs:6:26
|
6 | let s: Vec<String> = arg.iter().map(|s| String::from(s)).collect();
| ^^^ borrowed value does not live long enough
7 | do_something_else(arg);
8 | }
| - borrowed value only lives until here
|
note: borrowed value must be valid for the lifetime 'a as defined on the function body at 1:9...
--> src/lib.rs:1:9
|
1 | fn func<'a, T>(arg: Vec<Box<T>>)
| ^^
rust lifetime
edited Nov 26 '18 at 17:13
Shepmaster
161k16330474
asked Nov 26 '18 at 16:45
NirmanNirman
534
fn func<'a, T>(arg: Vec<Box<T>>)
where
String: From<&'a T>,
T: 'a,
{
let s: Vec<String> = arg.iter().map(|s| String::from(s)).collect();
do_something_else(arg);
}
fn do_something_else<T>(arg: Vec<Box<T>>) {}
The compiler complains that arg does not live long enough. Why though?
error[E0597]: `arg` does not live long enough
--> src/lib.rs:6:26
|
6 | let s: Vec<String> = arg.iter().map(|s| String::from(s)).collect();
| ^^^ borrowed value does not live long enough
7 | do_something_else(arg);
8 | }
| - borrowed value only lives until here
|
note: borrowed value must be valid for the lifetime 'a as defined on the function body at 1:9...
--> src/lib.rs:1:9
|
1 | fn func<'a, T>(arg: Vec<Box<T>>)
| ^^
rust lifetime
rust lifetime
edited Nov 26 '18 at 17:13
Shepmaster
161k16330474
asked Nov 26 '18 at 16:45
NirmanNirman
534
edited Nov 26 '18 at 17:13
Shepmaster
161k16330474
asked Nov 26 '18 at 16:45
NirmanNirman
534
edited Nov 26 '18 at 17:13
Shepmaster
161k16330474
edited Nov 26 '18 at 17:13
Shepmaster
161k16330474
edited Nov 26 '18 at 17:13
Shepmaster
161k16330474
161k16330474
asked Nov 26 '18 at 16:45
NirmanNirman
534
asked Nov 26 '18 at 16:45
NirmanNirman
534
asked Nov 26 '18 at 16:45
NirmanNirman
534
534
So you want to useargafter collecting the members intos? Else I would say useinto_iterand it's all done.
– hellow
Nov 26 '18 at 16:58
add a comment |
So you want to useargafter collecting the members intos? Else I would say useinto_iterand it's all done.
– hellow
Nov 26 '18 at 16:58
So you want to use
arg after collecting the members into s? Else I would say use into_iter and it's all done.– hellow
Nov 26 '18 at 16:58
So you want to use
arg after collecting the members into s? Else I would say use into_iter and it's all done.– hellow
Nov 26 '18 at 16:58
add a comment |
1 Answer
1
active
oldest
votes
The constraint String: From<&'a T>, with emphasis on the function's lifetime parameter 'a, would allow you to convert a reference to T to a String. However, the reference to the elements obtained from the iterator is more restrictive than 'a (hence, they do not live long enough).
Since the conversion is supposed to work fine for references of any lifetime, you may replace the constraint with a higher ranked trait bound (HRTB):
fn func<T>(arg: Vec<Box<T>>)
where
for<'a> String: From<&'a T>,
{
let s: Vec<String> = arg.iter().map(|s| String::from(s)).collect();
do_something_else(arg);
}
The use of From here to obtain an owned string is also not something I've seen in the wild. Perhaps you would be interested in the Display trait, so that you can call to_string():
fn func<T>(arg: Vec<Box<T>>)
where
T: Display,
{
let _: Vec<_> = arg.iter().map(|s| s.to_string()).collect();
// ...
}
See also:
- How do I write the lifetimes for references in a type constraint when one of them is a local reference?
- How does for<> syntax differ from a regular lifetime bound?
answered Nov 26 '18 at 17:04
E_net4E_net4
12.8k73872
add a comment |
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1 Answer
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1 Answer
1
active
oldest
votes
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oldest
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oldest
votes
The constraint String: From<&'a T>, with emphasis on the function's lifetime parameter 'a, would allow you to convert a reference to T to a String. However, the reference to the elements obtained from the iterator is more restrictive than 'a (hence, they do not live long enough).
Since the conversion is supposed to work fine for references of any lifetime, you may replace the constraint with a higher ranked trait bound (HRTB):
fn func<T>(arg: Vec<Box<T>>)
where
for<'a> String: From<&'a T>,
{
let s: Vec<String> = arg.iter().map(|s| String::from(s)).collect();
do_something_else(arg);
}
The use of From here to obtain an owned string is also not something I've seen in the wild. Perhaps you would be interested in the Display trait, so that you can call to_string():
fn func<T>(arg: Vec<Box<T>>)
where
T: Display,
{
let _: Vec<_> = arg.iter().map(|s| s.to_string()).collect();
// ...
}
See also:
- How do I write the lifetimes for references in a type constraint when one of them is a local reference?
- How does for<> syntax differ from a regular lifetime bound?
answered Nov 26 '18 at 17:04
E_net4E_net4
12.8k73872
add a comment |
The constraint String: From<&'a T>, with emphasis on the function's lifetime parameter 'a, would allow you to convert a reference to T to a String. However, the reference to the elements obtained from the iterator is more restrictive than 'a (hence, they do not live long enough).
Since the conversion is supposed to work fine for references of any lifetime, you may replace the constraint with a higher ranked trait bound (HRTB):
fn func<T>(arg: Vec<Box<T>>)
where
for<'a> String: From<&'a T>,
{
let s: Vec<String> = arg.iter().map(|s| String::from(s)).collect();
do_something_else(arg);
}
The use of From here to obtain an owned string is also not something I've seen in the wild. Perhaps you would be interested in the Display trait, so that you can call to_string():
fn func<T>(arg: Vec<Box<T>>)
where
T: Display,
{
let _: Vec<_> = arg.iter().map(|s| s.to_string()).collect();
// ...
}
See also:
- How do I write the lifetimes for references in a type constraint when one of them is a local reference?
- How does for<> syntax differ from a regular lifetime bound?
answered Nov 26 '18 at 17:04
E_net4E_net4
12.8k73872
add a comment |
The constraint String: From<&'a T>, with emphasis on the function's lifetime parameter 'a, would allow you to convert a reference to T to a String. However, the reference to the elements obtained from the iterator is more restrictive than 'a (hence, they do not live long enough).
Since the conversion is supposed to work fine for references of any lifetime, you may replace the constraint with a higher ranked trait bound (HRTB):
fn func<T>(arg: Vec<Box<T>>)
where
for<'a> String: From<&'a T>,
{
let s: Vec<String> = arg.iter().map(|s| String::from(s)).collect();
do_something_else(arg);
}
The use of From here to obtain an owned string is also not something I've seen in the wild. Perhaps you would be interested in the Display trait, so that you can call to_string():
fn func<T>(arg: Vec<Box<T>>)
where
T: Display,
{
let _: Vec<_> = arg.iter().map(|s| s.to_string()).collect();
// ...
}
See also:
- How do I write the lifetimes for references in a type constraint when one of them is a local reference?
- How does for<> syntax differ from a regular lifetime bound?
answered Nov 26 '18 at 17:04
E_net4E_net4
12.8k73872
The constraint String: From<&'a T>, with emphasis on the function's lifetime parameter 'a, would allow you to convert a reference to T to a String. However, the reference to the elements obtained from the iterator is more restrictive than 'a (hence, they do not live long enough).
Since the conversion is supposed to work fine for references of any lifetime, you may replace the constraint with a higher ranked trait bound (HRTB):
fn func<T>(arg: Vec<Box<T>>)
where
for<'a> String: From<&'a T>,
{
let s: Vec<String> = arg.iter().map(|s| String::from(s)).collect();
do_something_else(arg);
}
The use of From here to obtain an owned string is also not something I've seen in the wild. Perhaps you would be interested in the Display trait, so that you can call to_string():
fn func<T>(arg: Vec<Box<T>>)
where
T: Display,
{
let _: Vec<_> = arg.iter().map(|s| s.to_string()).collect();
// ...
}
See also:
- How do I write the lifetimes for references in a type constraint when one of them is a local reference?
- How does for<> syntax differ from a regular lifetime bound?
answered Nov 26 '18 at 17:04
E_net4E_net4
12.8k73872
edited Nov 27 '18 at 9:41
answered Nov 26 '18 at 17:04
E_net4E_net4
12.8k73872
answered Nov 26 '18 at 17:04
E_net4E_net4
12.8k73872
answered Nov 26 '18 at 17:04
E_net4E_net4
12.8k73872
12.8k73872
add a comment |
add a comment |
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So you want to use
argafter collecting the members intos? Else I would say useinto_iterand it's all done.– hellow
Nov 26 '18 at 16:58