in reply to I don't understand this grep

The following code 

sub channels_by_level { grep { $_[0]->level( $_[1] ) } $_[0]->channels
+ }

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can be written more clear such as: 

sub channels_by_level { 
    my $self  = shift;
    my $level = shift;
    return grep { $self->level( $level ) } $self->channels;
}

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Method $obj->channels_by_level($level) returns those channels which has level given in an argument.

The problem is that your object doesn't have channels. To understand why it doesn't more code need to be shown.

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Re^2: I don't understand this grep
by gone2015 (Deacon) on Nov 05, 2008 at 18:07 UTC

    The curious thing is that the test in the grep:

      return grep { $self->level( $level ) } $self->channels;

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    contains nothing that depends on whatever $self->channels is or returns. It could equally be written:
      return $self->level($level) ? $self->channels : () ;

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    but that doesn't answer the question of why $self->channels appears to be missing.

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      I wonder if it's supposed to be 
      return grep { $_->level( $level ) } $self->channels;

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        Yes it's easy to mess $_ and $_[0]. Nobody see that until an error occured.
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        I tried adjusting the syntax and got the exact same message. $self->channels is not defined anywhere in the module, so it is either misnamed or missing. I will have to figure that out

        g_White
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      Well, that won't work if $self->channels returns a list, which seems likely, based on the name.

      Update: Need to engage eyeballs before fingers. Thanks massa and jwkrahn for an appropriate whack on the side of the head.

      G. Wade
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        That should work fine.   What makes you think that it won't work?

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        ??!!!
        Yes it will work with channels returning a list, according to Conditional operator:
        Scalar or list context propagates downward into the 2nd or 3rd argument, whichever is selected.
        And it won't execute $self->level($level) once for each item of the returned list, which is good.

        Now, the reason why channels is missing is because... well, gwhite didn't show any sub channels { ... } in the module... But he didn't state that it does not exist, either...

        []s, HTH, Massa (κς,πμ,πλ)
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