[Issue 14984] Make it illegal (or at least a warning) to modify the iteration variable in foreach

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=14984

--- Comment #2 from Kenji Hara <k.hara.pg at gmail.com> ---
Currently it's intentional. When you declare a index variable in foreach
statement, it works like an auto variable scoped in the foreach body.

If you need non-mutable index variable, you can write code like:

foreach (const i, v; arr) { ... }
foreach (const i; 0..len) { ... }

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