What does this mean?

fritz1968 has asked for the wisdom of the Perl Monks concerning the following question:

I get to troubleshoot someone else's code. (yeah!). Anyhoo, I am trying to make sense of the following code:


package my_wsdl;

sub new {
    my $class = shift;
    my $self  = {
        _id               => shift,
        _client           => shift,
        _externalID       => shift,
        _externalParentId => shift,
        _provider         => shift,
        _action           => shift,
        _priority         => shift,
        _actionTime       => shift,
        _state            => shift,
        _result           => shift,
        _locked           => shift,
        _lockedTimes      => shift,
        _sid              => shift,
        _domain           => shift,
        _samAccountName   => shift,
    };

    bless $self, $class;
    return $self;
}

sub setID {
    my ( $self, $id ) = @_;
    $self->{_id} = $id if defined($id);
    return $self->{_id};
[download]

Specifically, in human terms, what does the following line mean?

$self->{_id} = $id if defined($id);
[download]

Thanks, Frank

Comment on What does this mean? Select or Download Code

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Re: What does this mean? by moritz (Cardinal) on Aug 20, 2012 at 19:51 UTC
It means if an argument was passed to `setID`, and it was defined (ie not undef), then set the attribute `_id` to that argument. Perl 6 - the future is here, just unevenly distributed	[reply] [d/l] [select]
Re: What does this mean? by Perlbotics (Archbishop) on Aug 20, 2012 at 19:55 UTC
It's a common setter/getter idiom however with an unfortunate chosen method name `setID`. 'get' attribute: no argument given, so $id is undefined, current value of `$self->{_id}` is returned `my $id = $obj->setID(); # return current _id` [download] 'set' attribute (and 'get' new value at the same time) `my $new_id = $obj->setID( 42 ); # updates and returns new _id 42 # or just: $obj->setID( 42 );` [download]	[reply] [d/l] [select]
Re^2: What does this mean? by tobyink (Canon) on Aug 20, 2012 at 22:24 UTC
I don't know if it was necessarily intended to act as a getter+setter. It's probably just a setter that happens to include a quick check to prevent people from setting the ID to undef. It happens to also return the current ID, but I'd assume that's just incidental. A method needs to return something; might as well be something vaguely useful. `perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'`	[reply]
Re: What does this mean? by bulk88 (Priest) on Aug 20, 2012 at 22:28 UTC
A statement "if" is not an operator or expression. Think of it as a block control keyword. Its precedence is dead last, below a ',', '=', '(', '[', '{', and '=>'. Last I played with it, if you try to treat it like an expression op, it will syntax error on you. If you see a statement if, in your head replace the "X if Y" with psuedo code "{X} if (Y)", any existing commas and parenthesis are irrelevant.	[reply]
Re: What does this mean? by Anonymous Monk on Aug 20, 2012 at 20:05 UTC
You could have written it this way: `if (defined($id)) { $self->{_id} = $id; }` [download] ... but this way's shorter. Perl is full of little "shortcuts" like that.	[reply] [d/l]
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