Clarified why Sized bound not implicit on trait's implicit Self type.
#48210
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src/libcore/marker.rs
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| /// The one exception is the implicit `Self` type of a trait. A trait does not | ||
| /// have an implicit `Sized` bound as this is incompatible with [trait object]s | ||
| /// where, by definition, one cannot know the size of all possible | ||
| /// implementations of the trait. |
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👍 for explaining why trait objects are not Sized.
I think the compiler would "know" the size of all implementations. But it's not something that is encoded in trait objects? Is there a clearer way to phrase this?
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It's especially important for public traits, since those are truly open-ended. If you're using a trait object, then that function needs to be treated as if the variable that's holding it has a single size, but if the trait is public, some new struct from downstream could come along that's a different size from what was expected. Perhaps something like this?
...with trait objects, which need to work with any implementor of the trait, and thus can be any size.
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I agree with both comments that this could be clearer. I've changed this slightly and, although more wordy, seems to read a bit better. What do you think?
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Looks great, thanks so much! @bors r+ rollup |
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📌 Commit 38064a9 has been approved by |
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…_api_docs, r=QuietMisdreavus Clarified why `Sized` bound not implicit on trait's implicit `Self` type. This part of the documentation was a little confusing to me on first read. I've added a couple lines for further explanation. Hopefully this makes things a bit clearer for new readers.
This part of the documentation was a little confusing to me on first read. I've added a couple lines for further explanation. Hopefully this makes things a bit clearer for new readers.
r? @steveklabnik