Unused variables, better as error or warning?

[bearophile]

Walter Bright:

> Not every problem is worth using a sledgehammer to deal with.

Giving a warning where you have not used a variable is not a sledgehammer, it's a light thing, that helps keep code tidy and once in a while helps avoid bugs.

I have not your experience with the troubles caused by warnings, so the last word is of course yours.

But I have another idea, static reflection, similar to the one in the Mozilla Treehydra project. DMD may add a __traits(allVariables, foo) that lists all variables used inside the function foo, and then another __traits(unusedVariable, foo, x) that returns true or false if the variable x inside the function foo is never used :-)

With few similar traits used by a (even in Phobos, if you want) library it's possible to analyse code and implement warnings as desired.

This static reflection, combined with user defined @attributes allows to create simple extensions to the type system, as Treehydra does, but with no need to use another language (as JavaScript, used by the Mozilla project).

Bye,
bearophile