Add must_use to the Reference
#35754
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Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @Manishearth (or someone else) soon. If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes. Please see the contribution instructions for more information. |
| @@ -2070,6 +2070,9 @@ macro scope. | |||
| trait of the same name. `{Self}` will be replaced with the type that is supposed | |||
| to implement the trait but doesn't. To use this, the `on_unimplemented` feature gate | |||
| must be enabled. | |||
| - `must_use` - on structs and enums, requires that instances are either consumed | |||
| or passed outside the crate. Using the full version `#[must_use = "message"]` | |||
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two things
- "consumed or passed outside the crate" is not 100% accurate here. "consumed" means something specific in Rust, I would say something more like "will warn if this value isn't bound to a variable."
- rather than "full version" I would say "You can additionally pass a message with this syntax that allows you..."
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The crate isn't actually important here?
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@Manishearth On second thought, you're absolutely right. I guess I was reading too into the lint that emitted the warning.
@steveklabnik I like that! I'll get that written in.
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r=me -- could you squash the two commits? |
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There you go, should be all set now. |
| @@ -2070,6 +2070,9 @@ macro scope. | |||
| trait of the same name. `{Self}` will be replaced with the type that is supposed | |||
| to implement the trait but doesn't. To use this, the `on_unimplemented` feature gate | |||
| must be enabled. | |||
| - `must_use` - on structs and enums, will warn if this value isn't bound to a variable. | |||
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This has little to do with binding to variables - after all, .unwrap() makes the warning go away
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Well, both work, because they both count as "use" . It's hard not to get circular here...
On Aug 17, 2016, 14:22 -0400, Jonas Schievink [email protected], wrote:
In src/doc/reference.md (#35754 (comment)):
@@ -2070,6 +2070,9 @@ macro scope. > trait of the same name.
{Self}will be replaced with the type that is supposed > to implement the trait but doesn't. To use this, theon_unimplementedfeature gate > must be enabled. > +-must_use- on structs and enums, will warn if this value isn't bound to a variable.This has little to do with binding to variables - after all, .unwrap() makes the warning go away
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"will warn when a function returning such a value is called without the returned value being used or assigned to a variable"
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But isn't What does actually warn is an expression statement some_fn(my_var) a use of my_var, too? This doesn't warn, however.<expr>; where <expr> has a #[must_use] type.
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I guess what I'm getting at is that "isn't bound to a variable" is a necessary but not sufficient requirement for the lint to fire.
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I would argue that some_fn(my_var) is a use under @Manishearth's version. It feels a little vague to put "isn't used" without refining it further, but at the same time trying to define what a "use" is feels like it would get overly wordy. Maybe "will warn when this value isn't used or assigned to a variable"?
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Possibly "will warn when a value of this type isn't used or assigned to a variable"?
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I like it, I'll use that version.
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@bors: r=Manishearth rollup |
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📌 Commit 0384722 has been approved by |
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Sorry for missing this! (I have the time to review things, just ping me in two days if I forget) |
… r=Manishearth Add `must_use` to the Reference I'm a bit uncertain about the exact phrasing, but having it mentioned at all is probably better than before.
… r=Manishearth Add `must_use` to the Reference I'm a bit uncertain about the exact phrasing, but having it mentioned at all is probably better than before.
… r=Manishearth Add `must_use` to the Reference I'm a bit uncertain about the exact phrasing, but having it mentioned at all is probably better than before.
I'm a bit uncertain about the exact phrasing, but having it mentioned at all is probably better than before.