digitalmars.D.bugs - [Issue 24395] New: Allow braced statements in loop conditions
- d-bugmail puremagic.com (43/43) Feb 14 https://issues.dlang.org/show_bug.cgi?id=24395
https://issues.dlang.org/show_bug.cgi?id=24395 Issue ID: 24395 Summary: Allow braced statements in loop conditions Product: D Version: D2 Hardware: All OS: All Status: NEW Severity: enhancement Priority: P1 Component: dmd Assignee: nobody puremagic.com Reporter: qs.il.paperinik gmail.com For loops allow a braced sequence of statements in the first section: ```d // Valid D code: for ({int i = 1; int n = 10;} i < n; ++i) { } ``` Variables declared there are visible in the following two sections and the loop body. I propose to allow this for the condition as well: Like the initial section, the condition could be a braced sequence of statements, where the last statement would be special-cased in the sense that it must evaluate to something that can be interpreted as a Boolean condition. E.g.: ```d // Proposed D code: for (int i = 0; {int n = 10 - i; i < n;} ++i) { } ``` The main difference between this and an immediately invoked lambda is probably scope: The braces as part of the `for` loop construct do not create a scope; the variable `n` in the example would be visible in the condition, the increment (what `++i` is) and the body of the for loop. It would make sense to allow the same for the condition of the `while` loop. That allows e.g. to rewrite the standard C `fgetc` pattern in a cleaner fashion: ```d while ({int c = std::fgetc(fp); c != EOF;}) { ... } ``` To be consistent, it should also work on a `do…while` loop, albeit not being that useful as the scope of variables declared in its condition should not be visible in the loop body. --
Feb 14