Re: Why callbacks?

No need for globals, just have the coderef use lexicals in the scope it's declared in (i.e. use a closure).

{
my $returned_data = [ ];

sub my_fetch_callback { push @{ $returned_data }, $_[0] }

routine_wanting_callback( \&my_fetch_callback );

for my $datum ( @{ $returned_data } ) {
  munge_it( $datum );
}
}
[download]

Update: Moved bracket after for so it would, you know, actually work. Duurr. Stupid trees making pollen affecting sinuses with their pollen making brane numbing congestion stuff.

Another example: You could also pass a coderef which stores the results by calling methods on an object you provide.

my $line_holder = Line::Holding->new( );

routine_wanting_callback( sub { $line_holder->hold( $_[0] ) } );

$line_holder->process_held_lines;
[download]

Nothing says the callback has to call a named subroutine sitting in the symbol table (unless the callback wanting routine says it takes the name of a subroutine of course; but that'd just be bad design :).

Comment on Re: Why callbacks? Select or Download Code

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Re^2: Why callbacks? by pileofrogs (Priest) on Mar 30, 2007 at 17:19 UTC
Woah... doesn't my_fetch_callback go out of scope before you can call it?	[reply]
Re^3: Why callbacks? by Joost (Canon) on Mar 30, 2007 at 17:32 UTC
Named subroutines never go out of scope; they're global - bound to a package just like global variables. Anonymous subrefs can go out of scope, just like any other variable, but, just like any other variable, you can pass them around: `sub call { my ($arg1,$arg2) = @_; my $callback = sub { my ($arg3) = @_; return $arg1 + $arg2 + $arg3; }; call_func_needing_callback($callback); } # or even sub call { my ($arg1,$arg2) = @_; call_func_needing_callback( sub { my ($arg3) = @_; return $arg1 + $arg2 + $arg3; }); }` [download] Also note that there are scoping issues with defining named closures within other subroutines (this probably has to do with named subroutines being global), while unnamed subroutines/closures will work as real lexical closures. "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply] [d/l]
Re^3: Why callbacks? by Fletch (Bishop) on Mar 30, 2007 at 17:27 UTC
I presume this was asked before I moved the brace, but even then no. The scalar would have (which is why I made the correction), but the subroutine sticks around (they're not lexically declared). Had I done this: `{ my $returned_data = []; my $callback = sub { push @{ $returned_data }, $_[0] }; } something_wanting_callback( $callback );` [download] Then yes, that coderef would have gone out of scope.	[reply] [d/l]
Re^4: Why callbacks? by pileofrogs (Priest) on Mar 30, 2007 at 17:32 UTC
So, all subrutines are in effect global? Huh.. I didn't know that. -Pileofrogs In Other News: Whoever keeps downvoting me, please tell me what it is that you don't like... I can't get better if you don't tell me what's wrong...	[reply]
Re^5: Why callbacks? by Fletch (Bishop) on Mar 30, 2007 at 17:41 UTC


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