make IndexMut a super trait over Index
#21949
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@bors r+ 5270eac 👍 |
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closes #21630 Overloaded indexing (`&[mut] foo[bar]`) only works when `<Self as Index>::Output` is the same as `<Self as IndexMut>::Output` (see issue above). To restrict implementations of `IndexMut` that doesn't work, this PR makes `IndexMut` a supertrait over `Index`, i.e. `trait IndexMut<I>: Index<I>`, just like in the `trait DerefMut: Deref` case. This breaks all downstream implementations of `IndexMut`, in most cases this simply means removing the `type Output = ..` bit, which is now redundant, from `IndexMut` implementations: ``` diff impl Index<Foo> for Bar { type Output = Baz; .. } impl IndexMut<Foo> for Bar { - type Output = Baz; .. } ``` [breaking-change] --- r? @nikomatsakis
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closes #21630
Overloaded indexing (
&[mut] foo[bar]) only works when<Self as Index>::Outputis the same as<Self as IndexMut>::Output(see issue above). To restrict implementations ofIndexMutthat doesn't work, this PR makesIndexMuta supertrait overIndex, i.e.trait IndexMut<I>: Index<I>, just like in thetrait DerefMut: Derefcase.This breaks all downstream implementations of
IndexMut, in most cases this simply means removing thetype Output = ..bit, which is now redundant, fromIndexMutimplementations:impl Index<Foo> for Bar { type Output = Baz; .. } impl IndexMut<Foo> for Bar { - type Output = Baz; .. }[breaking-change]
r? @nikomatsakis