Document that type parameter `Self` is maybe-sized by default #1285

fmease · 2022-10-19T09:57:56Z

The (implicit) type parameter Self in traits is not Sized by default but the current documentation is not very clear about it.

All type parameters have an implicit bound of Sized. […] The one exception is the implicit Self type of a trait.

Source: Documentation of std::marker::Sized:

It's except Self in traits specifically since e.g. the “sizedness” of Self in structs depends on the sizedness of the last field.

As an aside, in general not much is written about Self in the reference. That's why I chose this specific location in the docs.

fmease · 2022-11-15T17:58:40Z

Is there anything I can do to push this PR forward? Do you generally like or dislike this clarification? Do you think this is the right place?

As for a wider context, when working on fixing rust-lang/rust#24183, I took a look into the Reference to make sure I was doing the right thing but I left a bit confused since I couldn't find anything about the relation between Self and Sized. That's why I created this patch.

ehuss

Thanks!

Update books ## rust-lang/book 1 commits in 3f64052c048c6def93b94a2b514ee88bba918744..a60f4316ec923a5ac2ed6a2eba6960edb832d855 2022-11-16 15:07:18 UTC to 2022-11-16 15:07:18 UTC - Fix Install MdBook command (rust-lang/book#3424) ## rust-embedded/book 4 commits in c533348edd69f11a8f4225d633a05d7093fddbf3..19f798d448835a4888e3b3eae7fe69f1d61d8681 2022-11-17 15:08:11 UTC to 2022-11-08 23:27:57 UTC - start/hardware.md: Fix typo (rust-embedded/book#336) - doc: Fix `arm-none-eabi-gdb` installation instruction for Fedora 27 or newer to just use `gdb` (rust-embedded/book#335) - Update singletons.md (rust-embedded/book#334) - Remove incorrect claim HashMap is avail in no_std (rust-embedded/book#333) ## rust-lang/nomicon 2 commits in 05532356e7a4dbea2330aabb77611f5179493bb8..ae406aa5287a9e025abb72343aaceec98458c117 2022-11-21 22:48:20 UTC to 2022-11-15 00:29:20 UTC - Improve chapter about `Vec<T>` (rust-lang/nomicon#381) - Grammar change for 3.4: Limits of Lifetimes (lifetime-mismatch.md) (rust-lang/nomicon#386) ## rust-lang/reference 9 commits in 9f0cc13ffcd27c1fbe1ab766a9491e15ddcf4d19..3ae62681ff236d5528ef7c8c28ba7c6b2ecc6731 2022-12-05 00:51:50 UTC to 2022-11-15 20:43:30 UTC - Document that type parameter `Self` is unsized by default (rust-lang/reference#1285) - replace `crateid` term with `crate_name` (rust-lang/reference#1310) - Document native library modifier `verbatim` (rust-lang/reference#1299) - Update literal suffix docs for rust-lang#102944 (rust-lang/reference#1305) - update aliasing rules section of the reference (rust-lang/reference#1290) - Document RFC 2867: instruction_set attribute (rust-lang/reference#1253) - Fix a minor typo in the "Higher-ranked trait bounds" section (rust-lang/reference#1288) - Disallow newline directly following `//` (rust-lang/reference#1294) - Add an anchor to the "forwarding macro fragments" paragraph (rust-lang/reference#1300) ## rust-lang/rust-by-example 5 commits in 2b15c0abf2bada6e00553814336bc3e2d8399097..a9869b4a3c4cac3bc6099b41f088679e268400b8 2022-11-27 19:03:05 UTC to 2022-11-11 18:54:53 UTC - Migrate from highfive to triagebot (rust-lang/rust-by-example#1647) - Simpler version of the read_lines script. (rust-lang/rust-by-example#1641) - Fix comment in "Formatted print" example code (rust-lang/rust-by-example#1638) - Added a missing backtick in a comment in chapter 15.4. (rust-lang/rust-by-example#1642) - Clarify the confusing closure example rust-lang#1611 (rust-lang/rust-by-example#1643) ## rust-lang/rustc-dev-guide 13 commits in d0dc6c97a6486f68bac782fff135086eae6d77ec..e269950a57fa6fcda356426545fb5aa3691a7ced 2022-12-03 23:09:24 UTC to 2022-11-08 21:35:38 UTC - Remove duplicate paragraph (rust-lang/rustc-dev-guide#1523) - clarify subtree tool policy (rust-lang/rustc-dev-guide#1518) - Typo (rust-lang/rustc-dev-guide#1520) - Link directly to the section on `--keep-stage` (rust-lang/rustc-dev-guide#1515) - do an actual link to detect if it breaks in future (rust-lang/rustc-dev-guide#1517) - Triage some date-check items (rust-lang/rustc-dev-guide#1513) - Update path for `try_mark_green` implementation (rust-lang/rustc-dev-guide#1512) - Fix a broken design docs link about unused substs bug (rust-lang/rustc-dev-guide#1511) - updating-llvm: keep a calm tone (rust-lang/rustc-dev-guide#1449) - date-check: updating-llvm (rust-lang/rustc-dev-guide#1424) - rewrite the section about regions in the trait solver (rust-lang/rustc-dev-guide#1508) - Consistent ordered list indexing (rust-lang/rustc-dev-guide#1509) - Document multiple alternative suggestions on diagnostic structs (rust-lang/rustc-dev-guide#1486)

fmease changed the title ~~Type parameter Self is unsized by default~~ Document that type parameter Self is unsized by default Oct 19, 2022

type parameter Self is unsized by default

50a597c

fmease force-pushed the self-is-unsized-by-default branch from 1bc6279 to 50a597c Compare October 20, 2022 10:40

ehuss approved these changes Dec 5, 2022

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ehuss merged commit 3ae6268 into rust-lang:master Dec 5, 2022

fmease deleted the self-is-unsized-by-default branch December 5, 2022 00:57

rustbot mentioned this pull request Dec 5, 2022

Update books rust-lang/rust#105313

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fmease changed the title ~~Document that type parameter Self is unsized by default~~ Document that type parameter Self is maybe-sized by default Feb 21, 2023

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Document that type parameter `Self` is maybe-sized by default #1285

Document that type parameter `Self` is maybe-sized by default #1285

fmease commented Oct 19, 2022 •

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fmease commented Nov 15, 2022 •

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Document that type parameter Self is maybe-sized by default #1285

Document that type parameter Self is maybe-sized by default #1285

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Document that type parameter `Self` is maybe-sized by default #1285

Document that type parameter `Self` is maybe-sized by default #1285

fmease commented Oct 19, 2022 •

edited

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fmease commented Nov 15, 2022 •

edited

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