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Update an outdated comment in mir building #56127

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Merged
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Update an outdated comment in mir building #56127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Update an outdated comment in mir building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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7 changes: 4 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 +85,10 @@ 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
// entire constant. Thus we do not drop these temporaries and simply leak them.
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Not "entire constant". The semantics of shallow temporaries in the RHS of a binding is that they escape into the ambient scope. For a const/static, this ambient scope is 'static.

// 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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