fix: More accurate lifetime bounds on scoped methods to allow valid code to compile #919
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…ode to compile Prior to this change, it was impossible to escape a value in `execute_scoped` that was created in an outer scope. This is because the function definition allowed for the outer and inner lifetimes to be entirely unrelated. This is technically a breaking change, but in many cases the more strict bound will cause code to be more likely to compile.
kjvalencik
commented
Jul 22, 2022
| env: Env, | ||
| phantom_inner: PhantomData<&'a ()>, | ||
| phantom_outer: PhantomData<&'outer ()>, |
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This was required before to ensure that ComputeContext couldn't accidentally outlive the outer context. However, compute_scoped now includes a 'a: 'b bound that provides the same guarantee.
kjvalencik
commented
Jul 22, 2022
| @@ -242,9 +242,10 @@ pub trait Context<'a>: ContextInternal<'a> { | |||
| /// Handles created in the new scope are kept alive only for the duration of the computation and cannot escape. | |||
| /// | |||
| /// This method can be useful for limiting the life of temporary values created during long-running computations, to prevent leaks. | |||
| fn execute_scoped<T, F>(&mut self, f: F) -> T | |||
| fn execute_scoped<'b, T, F>(&mut self, f: F) -> T | |||
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This change doesn't provide as much tangible value, but I thought it was good to keep them aligned.
dherman
approved these changes
Jul 22, 2022
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Prior to this change, it was impossible to escape a value in
execute_scopedthat was created in an outer scope. This is because thefunction definition allowed for the outer and inner lifetimes to be entirely unrelated.
This is technically a breaking change, but in many cases the more strict bound will cause code to be more likely to compile.
The following code compiles after this change, but not before: