Mike Lesser wrote:
Hiya. I'm looking for the correct Perl style for testing and storing a
return value in a control statement. The solution in any other language
is pretty obvious, but I get the distinct impression that there's a
'right' way in Perl...
Let's say I want to test a scalar returned from a subroutine, and also
keep a copy for my own use:
$scalar = sub( $argument );
if( $scalar ){
}
Naturally that's no big deal. Now let's say I have a tree I want to
traverse, or some similar open-ended thing to evaluate, and want to run
it until a condition is reached..
while( read_tree( $argument ){
}
Again no biggie. The problem is if I want to keep the result. Obviously
I can't do this:
while( $tree_element = read_tree( $argument ) ){
do_something( $tree_element );
}
I can come up with a brute-force solution of course, but there's
probably a better, Perlish way that I'm not aware of. In addition, I
don't expect a return value from some module to be consistently
undefined or zero; it could change under some circumstances. This makes
me think that the problem has been dealt with long ago, and just doesn't
stick out in the llama/alpaca/whatever books.
Hopefully I explained this correctly!
while (my $x = func()) {
:
}
is perfectly valid. In Perl every operator returns a value, and the assignment
operator is no exception. It's value is the expression on the left of the equals
sign, and it's even an lvalue so you can do things like
($x = 3)++;
leaving $x with a value of four. This sort of thing is more useful for things
like
$p = $q = 'A';
which is the same as
$p = ($q = 'A');
or
$q = 'A'; $p = $q;
But the bottom line is that your while loop is quite valid.
HTH,
Rob
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