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Update an outdated comment in mir building #56127

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merged 3 commits into from
Nov 29, 2018
Merged

Update an outdated comment in mir building #56127

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83388e8
Update an outdated comment in mir building
oli-obk Nov 21, 2018
5a2a251
Update as_temp.rs
oli-obk Nov 21, 2018
925274a
Update as_temp.rs
oli-obk Nov 21, 2018
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12 changes: 9 additions & 3 deletions src/librustc_mir/build/expr/as_temp.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -85,9 +85,15 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {

unpack!(block = this.into(&Place::Local(temp), block, expr));

// In constants, temp_lifetime is None. We should not need to drop
// anything because no values with a destructor can be created in
// a constant at this time, even if the type may need dropping.
// In constants, temp_lifetime is None for temporaries that live for the
// 'static lifetime. Thus we do not drop these temporaries and simply leak them.
// This is equivalent to what `let x = &foo();` does in functions. The temporary
// is lifted to their surrounding scope. In a function that means the temporary lives
// until just before the function returns. In constants that means it outlives the
// constant's initialization value computation. Anything outliving a constant
// must have the `'static` lifetime and live forever.
// Anything with a shorter lifetime (e.g the `&foo()` in `bar(&foo())` or anything
// within a block will keep the regular drops just like runtime code.
if let Some(temp_lifetime) = temp_lifetime {
this.schedule_drop_storage_and_value(
expr_span,
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