Improve Type-Coersion Documentation #843
Conversation
| @@ -91,7 +95,7 @@ the block has a known type. | |||
|
|
|||
| Coercion is allowed between the following types: | |||
|
|
|||
| * `T` to `U` if `T` is a subtype of `U` (*reflexive case*) | |||
| * `T` to `U` if `T` is a [subtype] of `U` (*reflexive case*) | |||
There was a problem hiding this comment.
There seems to be an unanswered question here: https://github.com/rust-lang/reference/pull/342/files#r191050490
There was a problem hiding this comment.
I've had little experience with the term 'reflexive' in programming contexts, but in math, "is a subset of" is a reflexive relationship. I assume that "is a subtype of" would be the programming equivalent.
There was a problem hiding this comment.
Ah. I'm not super familiar with it, but since this is just adding a link, I won't hold up the PR on it. AIUI, the reflexive subtype would be "T is a subtype of T", not U (in the math sense, T is a subset of T).
There was a problem hiding this comment.
I guess.. Subtyping is an example of a reflexive relationship, because types are subtypes of themselves. So.. That means that a subtype coersion is reflexive, because it could be coercing to Self. That sounds really finicky now that I say it.
|
@ehuss What's the verdict on this? |
src/type-coercions.md
Outdated
| The [type cast operator], `as`, is not a coersion site. However, most type | ||
| conversions allowed by coersion can also be explicitly performed by `as`. |
There was a problem hiding this comment.
The phrasing here seems a little strange to me. Nothing suggests or implies that as is a coercion site. The equivalence doesn't make sense because as is an expression, not a location. It also says "most type conversions...", but then doesn't say which are allowed.
I think it would be best just to keep this simple and to the point. I still suggest my original wording, something like For explicit type coercions, see [type cast expressions]..
Also, the word is spelled "coercion" with a c.
There was a problem hiding this comment.
I'm trying to make the distinction that, if it's explicit, it's not a coercion. You're right that that wording is funky, though.
| The [type cast operator], `as`, is not a coersion site. However, most type | ||
| conversions allowed by coersion can also be explicitly performed by `as`. | ||
|
|
||
| Coercions are originally defined in [RFC 401] and expanded upon in [RFC 1558]. | ||
|
|
There was a problem hiding this comment.
Try to avoid double blank lines.
Update books ## reference 4 commits in 1b6c4b0afab97c0230433466c97167bbbe8445f6..25391dba46262f882fa846beefaff54a966a8fa5 2020-08-18 17:04:28 -0700 to 2020-09-02 07:22:55 -0700 - clarify when reading uninititalized memory is allowed (rust-lang/reference#852) - Update patterns chapter, add rest patterns. (rust-lang/reference#876) - Improve Type-Coersion Documentation (rust-lang/reference#843) - Added variable back into example. (rust-lang/reference#880) ## book 3 commits in c0a6a61b8205da14ac955425f74258ffd8ee065d..e5ed97128302d5fa45dbac0e64426bc7649a558c 2020-08-14 14:21:49 -0500 to 2020-08-31 12:53:40 -0500 - Fix type mismatch in listing 10-5 (rust-lang/book#2441) - Update ppendix-06-translation.md (rust-lang/book#2437) - Correct no-listing-10-result-in-tests: Take tests module out of the main function (rust-lang/book#2430) ## rust-by-example 3 commits in 80a10e22140e28392b99d24ed02f4c6d8cb770a0..19f0a0372af497b34369cf182d9d16156cab2969 2020-08-08 09:56:46 -0300 to 2020-08-26 09:38:48 -0300 - prefer `length` over `size` when talking about number of elements vs. bytesize (rust-lang/rust-by-example#1372) - Split out variable shadowing into a separate example (rust-lang/rust-by-example#1370) - Update extern crate related sections (rust-lang/rust-by-example#1369) ## edition-guide 1 commits in bd6e4a9f59c5c1545f572266af77f5c7a5bad6d1..81f16863014de60b53de401d71ff904d163ee030 2020-07-12 17:37:08 -0500 to 2020-08-27 13:56:31 -0700 - Fix a small typo. (rust-lang/edition-guide#218)
I've updated pull request #342 by @Havvy by fixing the merge conflicts, and additionally adding a fix to close #734 (Incorrect examples of type coercion).