Bug 15437 – documentation for typeof(someTemplate) == void

Consider this: auto tee(alias fun, Flag!"pipeOnPop" pipeOnPop = Yes.pipeOnPop, R1)(R1 inputRange) if (is(typeof(fun) == void) || isSomeFunction!fun); It is not immediately obvious in what situation `fun` would have (typeof(fun) == void) unless you know that templates received through an alias have typeof void, but there doesn't seem to be any place in the documentation mentioning that fact. Even if this is mentioned in the docs somewhere, it might still be worth redundantly mentioning this in more than one place. Consider the sections on AliasDeclaration and typeof (part of the declaration docs), and the Template docs.

IIRC, typeof(fun) gives the function's return type.

But if it is a function *template* then the type will be void. That's what could be better documented, IMHO.

Maybe it's not an intended behavior and type of template should be `template`?

Maybe something like this: T add(T)(T a, T b) { return a + b; } static assert (is(typeof(add) == template)); alias add2 = (a,b) => a + b; static assert (is(typeof(add2) == template)); ?

Though this would add overlap to the functionality already provided by http://dlang.org/spec/traits.html#isTemplate. Also related: https://github.com/D-Programming-Language/dmd/pull/5201

Related: https://issues.dlang.org/show_bug.cgi?id=7947 I briefly talked to both Andrei and Walter today at dconf about this. They both agreed, that calling typeof on a template should be an error (similiar to how calling typeof on a type is an error). Any thoughts on that?

preapproved

Realated comment in the corresponding section in dmd: /* Today, 'typeof(func)' returns void if func is a * function template (TemplateExp), or * template lambda (FuncExp). * It's actually used in Phobos as an idiom, to branch code for * template functions. */ Does anybody know where this is actually used in phobos? Wouldn't it be better to use isTemplate in this case?

@pbackus created dlang/dlang.org pull request #3218 "Fix issue 15437 - documentation for typeof(someTemplate) == void" fixing this issue: - Fix issue 15437 - documentation for typeof(someTemplate) == void https://github.com/dlang/dlang.org/pull/3218

dlang/dlang.org pull request #3218 "Fix issue 15437 - documentation for typeof(someTemplate) == void" was merged into master: - 5d5764f978d32dadaeed12afe3dd26992b822b9d by Paul Backus: Fix issue 15437 - documentation for typeof(someTemplate) == void https://github.com/dlang/dlang.org/pull/3218