Re: Far More than Everything You've Ever Wanted to Know about Prototypes in Perl -- by Tom Christiansenby perl-diddler (Hermit)
|on Sep 27, 2010 at 19:40 UTC||Need Help??|
I still like prototypes and wish they could be enforced (or generate a warning) at runtime, when used incorrectly, indirectly. I see that as the biggest limitation of the current implementation of 'parsing prototypes' -- that they are only enforced or only used during direct calls.
Everything else that the author complained about was a non-complaint *if* you follow the 1st 'best practice' (In my book) of turning on "-w" at the start.
All of the multi-prototypes like he shows would generate warnings. The only prototype 'gotcha', that really exists with the current prototype system -- that *could* be improved upon, with a language extension, is the situation of declaring a proto with sub foobar($); and then calling it with foo(@a) and expecting that to throw an error rather than evaluating the array in scalar context.
An additional warning could be added with some additional warning level (Warn-pedantic), to warn of implicit type conversions where a prototype was involved. You couldn't reasonably warn of implicit type conversions everywhere without alot of code rewrite, so turning on warning only for explicitly prototyped functions might be a reasonable 'by-request' addition to warnings.
Ideally, one might add an explicit type-cast operator syntax -- an extension of the 'wantarray' "question" operator -- where instead of just asking if an array is wanted in the return context, have some variation of wantarray that forces array interpretation instead of scalar.
I ran into a desire for this recently, where I had an array reference in a variable, but when I tried to use it with some operator that expected an array, it wouldn't work -- only by assigning it to an array first, would it work as I needed it to. But more important would be the ability to say 'want type (X)', before a var -- that way if one DID have warnings for prototypes that do implicit conversions, one could add the typecast to make the conversion explicit and eliminate the warning, like:
meaning a syntax that explicitly uses '@arr' in a scalar context so IF a warning for 'implicit conversions' with explicitly prototyped functions doing an implicit conversion was enabled, the warning could be silenced.
Similarly a warning could be made 'available' for assigning diverse types to a data structure or variable -- something that currently is allowed with no warning (it's a feature!) within a variable's scope -- like:
That would require clarification of lines like the assignment to @b. Did they really want @b to contain 3 elements, 2 scalars and a reference, or did they want @b to contain 2 references? Or inconsistent usages like:
The would certainly be for use with a particular type of coding practice, but one that would allow for only strictly typed-check usage.
Maybe it's not practical for some reason, but if it were, I could see it being useful for a more careful, more verbose style of programming -- perhaps it's already been done in some module?