there's no substite for using wantarray to check your calling context

Interesting example, though I fail to see how wantarray will help in this case:

sub use_wantarray { return wantarray ? () : 0 }
[download]

Wont work properly in your example either.... Note that the above sub is equivalent^* to the recommended way to return false, i.e. simply return:

sub recommended_way { return; }
[download]

^* except when used in void context, but that isn't relevant here.

-Blake