Hi

I'm puzzling over the best interface design of a multi-purpose function/operator, where the same function can be used for various purposes:

Lets take a function range() simulating the range operator as example:

 for ( range(1,9) ) { print $i }

 while ( range(1,9) ) {...}

 $f=range(1,9); while ( &$f ) {...}

should all do the same 9 loops.

The first two examples are easy to achieve by evaluating the context (for imposes list, while scalar context).

Unfortunately there is no "function context"...

I was thinking about blessing a scalar such that I can use scalar context for both cases, such that

 $f=range(1,9); while ( $i=$f->next ) {...} works.

Anyhow this is sabotaging performance, since calling methods on objects or ties is quite expensive... and I'm not sure if this double nature of $f could have ugly side effects.

The other approach would be using globs, such that calling *f=range(1,9); while ( $i=f() ) {...} would define a function f(), but ATM I'm not sure if this is even possible...and it shouldn't be working with lexical functions.

My best guess is to return a blessed scalar and to use this  $f=range(1,9)->iterator; while ( $i=&$f ) {...} ...

Any suggestions?

That's all untested code, hope you get the underlying ideas.

Cheers Rolf

PS: Yes I know that the while loops wouldn't work when range(0,9) is called, but thats another issue. I didn't want to over complicate the examples... :)

UPDATE:

After some meditation I think I got an even better idea, I could check for a third parameter to assign the scalar value to, such that in scalar context always a coderef is returned, this would also solve the "0 problem" (see PS):

 for my $i ( range(1,9) ) { print $i }

 while ( range 1,9 => my $i ) {...}

 $f=range(1,9); while ( $f->(my $i)) {...}

UPDATE:

I think I have to replace all mys with state restricting this feature to 5.10. 8(

In reply to Designing a DWIMish interface for generator function by LanX

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