Re: Redefine the sub of a subref?

Sounds like this might be a case for coderefs:

my $foo = sub { print "Foo\n"; };
my $bar = sub { print "Bar\n"; };
my $x = $foo;
$x->();  # prints "Foo"
$x = $bar;
$x->();  # prints "Bar"
[download]

Or, perhaps the same with a dispatch table:

my %code = (
    foo => sub { print "Foo\n"; },
    bar => sub { print "Bar\n"; },
);
$code{foo}();  # prints "Foo"
$code{bar}();  # prints "Bar"
[download]

Update: Combining that with Corion's excellent post:

sub bar {
    my( $output ) = @_;
    $output->();
}
my $foo1 = sub { print "Foo\n"; };
my $foo2 = sub { print "Bar\n"; };
bar( $foo1 );  # prints "Foo"
bar( $foo2 );  # prints "Bar"
[download]

Hope this helps,
-- Hauke D

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Re^2: Redefine the sub of a subref? by aplonis (Pilgrim) on Feb 05, 2017 at 03:34 UTC
Thank you both for those. I sure wouldn't have thought of either of those. I'll check them out later. Meanwhile, I also stubmled on this. It too seems to work. What the whole thing's about is that I have a DBI script with a Tk GUI. And that GUI... Well, it's one that auto-self-builds from a non-CPAN module named Tk::EasyGUI.pm which I wrote myself ten years ago. Meanwhile, I've done almost no Perl. And so, while I could still use it, and the GUI itself still worked great, I just couldn't seem to figure out what, quite exactly, was window/frame/sub-frame/pane/label/button reference to redefine -bind on. Which I needed to do so as to re-purpose a pair of buttons to each do two different things, depending on context. Hours I spent scratching my head, and then gave up. So then I decided, how much simpler it would be if only I could just redefine, dending on context, the subref which was the original callback for -bind on the auto-self-built GUI. Hence my call to gurus for help. And I do thank you. I'll try those out. Meanwhile, though, I managed to cobble this bit together, and thought maybe it might be worth adding into the thread. So my Tk has two buttons, X and Y. Normally they call DBI searches on date (X) or keyword (Y). But having called a search on keyword by pressing Y, I wanted the buttons for X to select, and Y to scroll to next. And to do it only while in a search on keyword, since that is the only one which can give plural rows. This is how, I made them do that (at least for now). Your other ways given are likely better, but this works for now. my $sql = "SELECT this, that, the_other FROM table WHERE foo = $bar"; my @rows; my $sth; my $ratchet_counter = 1; if ( $sth = $dbh->prepare($sql) ) { $sth->execute(); while ( @rows = $sth->fetchrow_array() ) { # Load in new values from current row. ( $this, $that, $the_other) = @rows; # Redefine button subs temporarily. local callback_X = sub { ++$ratchet_counter; }; # User wan +ting next row. local callback_Y = sub { $ratchet_counter = 0; }; # User cho +osing current row. $mw->waitVariable(\$ratchet_counter); # User mak +ing choice of show-next or keep-this. last if 0 == $rows_ratchet_index; # User made choice. } } else { $wgt->{'frame'}->{'entry'} = qq\|Oops! $DBI::errstr!\|; return (); } [download]	[reply] [d/l]

Replies are listed 'Best First'.

Re^2: Redefine the sub of a subref?
by aplonis (Pilgrim) on Feb 05, 2017 at 03:34 UTC

Thank you both for those. I sure wouldn't have thought of either of those. I'll check them out later. Meanwhile, I also stubmled on this. It too seems to work.

What the whole thing's about is that I have a DBI script with a Tk GUI. And that GUI... Well, it's one that auto-self-builds from a non-CPAN module named Tk::EasyGUI.pm which I wrote myself ten years ago. Meanwhile, I've done almost no Perl. And so, while I could still use it, and the GUI itself still worked great, I just couldn't seem to figure out what, quite exactly, was window/frame/sub-frame/pane/label/button reference to redefine -bind on. Which I needed to do so as to re-purpose a pair of buttons to each do two different things, depending on context. Hours I spent scratching my head, and then gave up. So then I decided, how much simpler it would be if only I could just redefine, dending on context, the subref which was the original callback for -bind on the auto-self-built GUI. Hence my call to gurus for help. And I do thank you. I'll try those out. Meanwhile, though, I managed to cobble this bit together, and thought maybe it might be worth adding into the thread.

So my Tk has two buttons, X and Y. Normally they call DBI searches on date (X) or keyword (Y). But having called a search on keyword by pressing Y, I wanted the buttons for X to select, and Y to scroll to next. And to do it only while in a search on keyword, since that is the only one which can give plural rows. This is how, I made them do that (at least for now). Your other ways given are likely better, but this works for now.

my $sql = "SELECT this, that, the_other FROM table WHERE foo = $bar";

my @rows;
my $sth;
my $ratchet_counter = 1;

if  ( $sth = $dbh->prepare($sql) ) {
    $sth->execute();
    while ( @rows = $sth->fetchrow_array() ) {
        
        # Load in new values from current row.
        ( $this, $that, $the_other) = @rows;
        
        # Redefine button subs temporarily.
        local *callback_X = sub { ++$ratchet_counter; };    # User wan
+ting next row.
        local *callback_Y = sub { $ratchet_counter = 0; };  # User cho
+osing current row.
            
        $mw->waitVariable(\$ratchet_counter);               # User mak
+ing choice of show-next or keep-this.
        
        last if 0 == $rows_ratchet_index; # User made choice.
    }
} else {
    $wgt->{'frame'}->{'entry'} = qq|Oops! $DBI::errstr!|;
    return ();
}
[download]

[reply]
[d/l]