context of printf ->wantarray

meyerti has asked for the wisdom of the Perl Monks concerning the following question:

hi. i'm trying to write context-sensitive subroutines using wantarray (or maybe Want). however when i call a subroutine from printf it fails like in sub t {return wantarray} printf "returns %i\n", t() ##returns 1 printf "returns %i\n", scalar t() ##returns 0 isn't there a way to pass the info of how many arguments printf expects to the subroutine without the explicit scalar? i hope my question is understandable, thanks for any help tim

Comment on context of printf ->wantarray

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Re: context of printf ->wantarray by moritz (Cardinal) on Nov 05, 2010 at 13:03 UTC
It's not wantarray() that fails, but an intrinsic problem in your approach: The arguments of a function are evaluated before the function is called. So in the case of `printf $format, subroutine()` the call to subroutine() is carried out before printf even had a chance to examine the $format argument. So even if it had a mechanism for signalling how many more arguments it needs, it would be too late for that. Instead it just always takes a list of arguments. So I suggest you try to find a different design that isn't based so heavily on introspection. Perl 6 - links to (nearly) everything that is Perl 6.	[reply] [d/l]
Re: context of printf ->wantarray by Fletch (Bishop) on Nov 05, 2010 at 13:28 UTC
Other advice aside you might check out Contextual::Return and make sure you're not reinventing wheels if you're determined to take this route. The cake is a lie. The cake is a lie. The cake is a lie.	[reply]
Re: context of printf ->wantarray by kcott (Archbishop) on Nov 05, 2010 at 13:00 UTC
I think you're maybe working from a false premise there. `printf` does want an array, so when you call `t()` in that context it returns TRUE (i.e. 1). When you specify `scalar`, it doesn't want an array and returns FALSE (i.e. 0). Take a look at the documentation for wantarray. -- Ken	[reply] [d/l] [select]