99d9ccd547
Go from
```
error[E0495]: cannot infer an appropriate lifetime due to conflicting requirements
--> file8.rs:22:5
|
22 | / move || {
23 | | *dest = g.get();
24 | | }
| |_____^
|
note: first, the lifetime cannot outlive the anonymous lifetime #1 defined on the function body at 18:1...
--> file8.rs:18:1
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18 | / fn bat<'a, G: 'a, T>(g: G, dest: &mut T) -> impl FnOnce() + '_ + 'a
19 | | where
20 | | G: Get<T>
21 | | {
... |
24 | | }
25 | | }
| |_^
note: ...so that the types are compatible
--> file8.rs:22:5
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22 | / move || { //~ ERROR cannot infer an appropriate lifetime
23 | | *dest = g.get();
24 | | }
| |_____^
= note: expected `&mut T`
found `&mut T`
note: but, the lifetime must be valid for the lifetime `'a` as defined on the function body at 18:8...
--> file8.rs:18:8
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18 | fn bat<'a, G: 'a, T>(g: G, dest: &mut T) -> impl FnOnce() + '_ + 'a
| ^^
note: ...so that return value is valid for the call
--> file8.rs:18:45
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18 | fn bat<'a, G: 'a, T>(g: G, dest: &mut T) -> impl FnOnce() + '_ + 'a
| ^^^^^^^^^^^^^^^^^^^^^^^
```
to
```
error[E0621]: explicit lifetime required in the type of `dest`
--> file8.rs:18:45
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18 | fn bat<'a, G: 'a, T>(g: G, dest: &mut T) -> impl FnOnce() + '_ + 'a
| ------ ^^^^^^^^^^^^^^^^^^^^^^^ lifetime `'a` required
| |
| help: add explicit lifetime `'a` to the type of `dest`: `&'a mut T`
```
101 lines
1.9 KiB
Rust
101 lines
1.9 KiB
Rust
pub trait Get<T> {
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fn get(self) -> T;
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}
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struct Foo {
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x: usize,
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}
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impl Get<usize> for Foo {
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fn get(self) -> usize {
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self.x
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}
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}
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fn foo<G, T>(g: G, dest: &mut T) -> impl FnOnce()
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where
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G: Get<T>
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{
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move || { //~ ERROR cannot infer an appropriate lifetime
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*dest = g.get();
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}
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}
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// After applying suggestion for `foo`:
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fn bar<G, T>(g: G, dest: &mut T) -> impl FnOnce() + '_
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//~^ ERROR the parameter type `G` may not live long enough
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where
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G: Get<T>
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{
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move || {
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*dest = g.get();
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}
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}
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// After applying suggestion for `bar`:
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fn baz<G: 'a, T>(g: G, dest: &mut T) -> impl FnOnce() + '_ //~ ERROR undeclared lifetime
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where
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G: Get<T>
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{
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move || {
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*dest = g.get();
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}
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}
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// After applying suggestion for `baz`:
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fn qux<'a, G: 'a, T>(g: G, dest: &mut T) -> impl FnOnce() + '_
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//~^ ERROR the parameter type `G` may not live long enough
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where
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G: Get<T>
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{
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move || {
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*dest = g.get();
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}
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}
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// After applying suggestion for `qux`:
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fn bat<'a, G: 'a, T>(g: G, dest: &mut T) -> impl FnOnce() + '_ + 'a
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//~^ ERROR explicit lifetime required in the type of `dest`
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where
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G: Get<T>
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{
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move || {
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*dest = g.get();
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}
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}
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// Potential incorrect attempt:
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fn bak<'a, G, T>(g: G, dest: &'a mut T) -> impl FnOnce() + 'a
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//~^ ERROR the parameter type `G` may not live long enough
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where
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G: Get<T>
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{
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move || {
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*dest = g.get();
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}
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}
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// We need to tie the lifetime of `G` with the lifetime of `&mut T` and the returned closure:
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fn ok<'a, G: 'a, T>(g: G, dest: &'a mut T) -> impl FnOnce() + 'a
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where
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G: Get<T>
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{
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move || {
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*dest = g.get();
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}
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}
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// This also works. The `'_` isn't necessary but it's where we arrive to following the suggestions:
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fn ok2<'a, G: 'a, T>(g: G, dest: &'a mut T) -> impl FnOnce() + '_ + 'a
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where
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G: Get<T>
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{
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move || {
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*dest = g.get();
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}
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}
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fn main() {}
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