http://qs321.pair.com?node_id=1232652


in reply to Re^2: Getting for() to accept a tied array in one statement
in thread Getting for() to accept a tied array in one statement

I disagree. Here is the full code and FETCH is only called once for each element within the body of the loop: 

use strict;
use warnings;

package MyClass;
    use Tie::Array;
    our @ISA = ('Tie::Array');
    our @data;
    # mandatory methods
    sub TIEARRAY { my $class = shift; bless \@data, $class; @data = @_
+; return \@data }
    sub FETCH { print "FETCH: "; my ($self, $index ) = @_; return $dat
+a[$index] }
    sub FETCHSIZE { print "<FETCHSIZE> "; return scalar @data }

package main;    
    
for( @{ tie my @x, "MyClass", "first", "second"; \@x } ) {
    print "In loop = ";
    print "$_\n";
}

[download]

Output: 

In loop = FETCH: first
In loop = FETCH: second

[download]

Replies are listed 'Best First'.
Re^4: Getting for() to accept a tied array in one statement
by perlancar (Hermit) on Apr 16, 2019 at 14:10 UTC

    Ah sorry, I stand corrected. I was reading your code as: for( do { tie my @x, "MyClass", "first", "second"; @x } ) {

    So indeed: for( @{ tie my @x, "MyClass", "first", "second"; \@x } ) {

    will make for() iterate over a tied array. In fact, 

    use strict;
use warnings;

package MyClass;
    use Tie::Array;
    our @ISA = ('Tie::Array');
        our @data;
    # mandatory methods
    sub TIEARRAY { my $class = shift; bless \@data, $class; @data = @_
+; return \@data }
    sub FETCH { print "FETCH: "; my ($self, $index ) = @_; return $dat
+a[$index] }
    sub FETCHSIZE { return scalar @data }

package main;

    sub wrapper {
        tie my @x, "MyClass", @_;
        \@x;
    }

for( @{wrapper("first", "second")} ) {
        print "In loop = ";
        print "$_\n";
}

    [download]

    also works. So it's quite close to what I want, yay. Any improvement is welcome :-)

[reply]
[d/l]
[select]

      Try this: 

          sub wrapper : lvalue {
        tie my @x, "MyClass", @_;
        @x;
    }

for( wrapper("first", "second") ) {
        print "In loop = ";
        print "$_\n";
}

      [download]

      As I said initially I am not expert in this, so there might be undesired side effects...

      And FETCHSIZE is called once only...

[reply]
[d/l]

        hdb, you're my hero :-) My faith in Perl is restored again.

[reply]

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