-
Notifications
You must be signed in to change notification settings - Fork 3.4k
New issue
Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.
By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.
Already on GitHub? Sign in to your account
ch19-06 added curly braces to macro output #2050
Conversation
I'm just learning rust (reading this book) so I might be wrong here... But shouldn't the generated macro-output include the extra curly braces?
If you add the curly braces then a scope would be created and the newly created vector would be dropped at the end of that scope. Since the vector exists after the macro expansion, the proposed equivalent code can't use curly braces (unless the owned result is returned from the macro). This will become more clear when ownership is discussed. If after my explanation you understand, then please also close the issue. |
Yes, but the vector is also returned by that scope... Let me illustrate my point with an example: let test = vec![1, 2, 3]; If the macro got unwrapped to what the book says this would become: let test = let mut temp_vec = Vec::new();
temp_vec.push(1);
temp_vec.push(2);
temp_vec.push(3);
temp_vec Whereas if it would become unwrapped the way I expect it to it would become: let test = {
let mut temp_vec = Vec::new();
temp_vec.push(1);
temp_vec.push(2);
temp_vec.push(3);
temp_vec
} which makes more sense to me. This also would explain the extra #[macro_export]
macro_rules! vec {
( $( $x:expr ),* ) => {
{ // <-- these ones
let mut temp_vec = Vec::new();
$(
temp_vec.push($x);
)*
temp_vec
} // <-- these ones
};
} |
As I said, "unless the owned result is returned"... I agree with the first part. Not sure what you mean in the second (extra curlies). I think they are connected to the way macros work. If it were plain Rust code, removing them would have no effect since the language is expression based. |
It's sorta tough because the actual macro calls a method these days: https://doc.rust-lang.org/stable/src/alloc/macros.rs.html#38-46 I do think the extra curlies make sense, but also, may be a bit distracting for others. I'm really torn. @carols10cents , any thoughts? |
I think the curly brackets make sense and won't be too confusing. Thanks! |
Update books. This required some changes in how the books are tested due to some changes in rust-lang/book. It uses new syntax that is not compatible with bare `rustdoc --test`. This changes it so that it uses rustbook to run the tests, which is essentially the same as `mdbook test`. ## reference 7 commits in 11e893f..64239df 2020-01-18 21:24:08 +0100 to 2020-02-10 19:05:13 +0100 - Update for nested receivers. (rust-lang/reference#724) - clarify note re. leading `::` in 2018 (rust-lang/reference#752) - Update macro-ambiguity.md (rust-lang/reference#754) - typo fix: add missing `by` (rust-lang/reference#753) - fix `TypeParamBounds` link on trait objects (rust-lang/reference#749) - reorganize docs on references (rust-lang/reference#745) - add MacroRepOp usage for ? (rust-lang/reference#744) ## book 49 commits in 87dd6843678575f8dda962f239d14ef4be14b352..6fb3705e5230311b096d47f7e2c91f9ce24393d0 2020-01-20 15:20:40 -0500 to 2020-02-12 13:48:57 -0500 - Fix nomicon links. (rust-lang/book#2253) - Update to Rust 1.41.0 (rust-lang/book#2244) - Listing 19-6: use ptr.add instead of ptr.offset (rust-lang/book#2201) - Remove unneeded mutable reference - Clarify deref coercion explanation - Fix typo in link to 1.30 book - Acknowledge Murphy's Law - Clarify that buffer overread is UB in C - Change from "must" to "idiomatic" about comments - Fancy quotes - Make HashMap types match previous example; add fwd ref to ch 13 - Tweak wording to array clarification - Merge remote-tracking branch 'origin/pr/2236' - Update all our crates (rust-lang/book#2235) - Reword git caveat - Merge remote-tracking branch 'origin/pr/2234' - Merge remote-tracking branch 'origin/pr/2230' - println! is a macro (rust-lang/book#2224) - Update a translated version link (rust-lang/book#2221) - move `Macro invocation` from section on tuple to section on mac… (rust-lang/book#2206) - Do not limit `Self` usage in trait implementation (rust-lang/book#2197) - Merge remote-tracking branch 'origin/pr/2191' - Fix wrapping - Merge remote-tracking branch 'origin/pr/2187' - Updated appendix 07 to reflect deprecation of rustup install (rust-lang/book#2181) - Make links to the Nomicon consistent - Merge remote-tracking branch 'origin/pr/2180' - Merge remote-tracking branch 'origin/pr/2175' - Merge remote-tracking branch 'origin/pr/2171' - Merge remote-tracking branch 'origin/pr/2170' - Clarify and make consistent the explanation of unions - Merge remote-tracking branch 'origin/pr/2166' - Handle dev or test in the Finished output line - Link to macros by example rather than macros (rust-lang/book#2164) - Merge remote-tracking branch 'origin/pr/2147' - Fix parens (rust-lang/book#2132) - Clarify type inference with closures requires calling the closures - Update link to French translation (rust-lang/book#2119) - Merge remote-tracking branch 'origin/pr/2108' - Add an explicit cross reference to data type - Merge remote-tracking branch 'origin/pr/2105' - ch15-02-deref: Improve explanation on immut-to-mut (rust-lang/book#2030) - Remove unnecessary quotes - Make markdown link identifier match - Remove extra newline - Merge remote-tracking branch 'origin/pr/2004' - Extract code and output; script formatting and updating them (rust-lang/book#2231) - Switch "Finally" to "Next" to reflect new chapters having been… (rust-lang/book#2098) - ch19-06 added curly braces to macro output (rust-lang/book#2050) ## rust-by-example 2 commits in 1c2bd024d13f8011307e13386cf1fea2180352b5..32facd5522ddbbf37baf01e4e4b6562bc55c071a 2020-01-20 12:18:36 -0300 to 2020-02-11 09:25:06 -0300 - Add missing `dyn` in code sample (rust-lang/rust-by-example#1306) - Improve grammar in a few sections (rust-lang/rust-by-example#1305) ## edition-guide 1 commits in 1a2390247ad6d08160e0dd74f40a01a9578659c2..37f9e6848411188a1062ead1bd8ebe4b8aa16899 2019-12-29 10:40:55 -0800 to 2020-02-10 14:36:14 +0100 - Fixed typo (rust-lang/edition-guide#196) ## embedded-book 4 commits in 4d78994915af1bde9a95c04a8c27d8dca066232a..b2e1092bf67bd4d7686c4553f186edbb7f5f92db 2020-01-14 08:25:25 +0000 to 2020-01-30 08:45:46 +0000 - Make typestate initialization notes correct (rust-embedded/book#224) - Mention discovery book more prominently (rust-embedded/book#219) - Replace nursery links with rust-lang links (rust-embedded/book#222) - Add a Glossary appendix page (rust-embedded/book#223)
I'm just learning rust (reading this book) so I might be wrong here...
But shouldn't the generated macro-output include the extra curly braces?