[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 #3 from Marc Schütz <schuetzm at gmx.net> ---
@Kenji Hara:

Yes, I know that. My point is that it's too easy to forget to add `const`.

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