David Hopwood writes:
> Torsten Anders wrote:
> >
> > Actually, when there is a variable you intent not to use (e.g. to comply
> > some given interface), you may just call it _.
>
> Erlang has a convention where variables that are intended to be unused have
> names starting with _ (including _ itself). The compiler warns only about
> non-use of variables that do not have a leading _. This is useful because
> the _ acts as documentation that the variable is not used, but has very low
> syntactic overhead.
>
> I like this convention much better than unconditionally warning about unused
> variables. In code that I write, unused variables are not infrequent, but
> *almost* always occur only for code that is unfinished (and obviously so), or
> for parameters that are intentionally not used by a particular implementation
> of a function/procedure/method.
>
Yes, I think this would be a good idea too, it is often good
documentation to give an unused var a name. I think Haskell does the
same. However, we have the additional issue that in Oz '_' can be used
anywhere to introduce a fresh unbound variable. So,
- Is '_X' equivalent to writing '_' or is it just a variable name that
bypasses the unused var check (or even is it a variable that is
introduced wthout declaration)?
i.e., in (case Exp of _X then {F _X} end) are they different vars or
the same?
- Can one write ..... {F _X _X} where _X is not in scope and introduce
a fresh var?
I think _X should be a first class variable name that only bypasses
the unused var check.
- Should the compiler warn when a variable starting with underscore
*is* used?
I am undecided, but I lean to yes.
cheers
k
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