Unused variables, better as error or warning?

[Nick Sabalausky]

"bearophile" <bearophileHUGS at lycos.com> wrote in message 
news:i4luk9$2rdg$1 at digitalmars.com...
>A small Reddit thread regarding if unused variables and imports are better 
>as errors or warnings:
> http://www.reddit.com/r/programming/comments/d3emo
>
> In my opinion in this case errors are too much, warning are enough.
>
> Few situations for those warnings:
> - warning for unused variables (as GC, C# and other compilers do);
> - warning when a variable get used in some ways, and then its last 
> assignment gets unused (done by a kind of C compiler);
> - unused imports (useful to keep code clean and remove unnecessary module 
> dependences);
> - unused functions (but this is harder to do in a clean way in a language 
> that has templates, so this may be omitted).
>
> Among those four warnings the most useful are the first two ones. In C 
> once the unused variable warning of GCC has found at compile time a bug in 
> my code (I did forget to increment that variable in the loop). So I have 
> loved this warning ever since.
>

An error would be an enormous pain in the ass. A warning might be helpful in 
some cases.