Contributed by draco_iii
on Jun 23, 2000 at 19:53 UTC
Q&A
> subroutines
Description: I have a routine that can return different information
depending on what kind of varible is asked of it.
If asking for a $ it returns a single set of
data, if you ask for an @ it will return the array.
But I can also have it return the information in a
hash format. I've thought about passing the varible
as a reference thinking that this would be a better
way to determine it.
Is this possible? Answer: How do you test for return type($,@,%)?
contributed by davorg A subroutine can only return a scalar or a list. What
the caller does with the result is completely out of the
subroutine's control.
For example:
sub array {
return 0 .. 5;
}
my %hash = array();
However, you _could_ do something like the code
below, but it's pretty strange stuff and I'm not
sure how useful it is :-)
#!/usr/bin/perl -w
use strict;
sub get_stuff {
my $ref = shift;
if (ref $ref) {
if (ref $ref eq 'SCALAR') {
$$ref = 'This is a scalar';
} elsif (ref $ref eq 'ARRAY') {
@$ref = qw(This is an array);
} elsif (ref $ref eq 'HASH' ) {
%$ref = (1 => 'This',
2 => 'is',
3 => 'a',
4 => 'Hash');
} else {
die "Invalid reference type passed to get_stuff.\n";
}
} else {
die "Non-reference passed to get_stuff.\n";
}
}
my ($scalar, @array, %hash);
get_stuff(\$scalar);
get_stuff(\@array);
get_stuff(\%hash);
print "$scalar\n";
$"='|';
print "@array\n";
print map { $hash{$_} . ' ' } sort keys %hash;
| Answer: How do you test for return type($,@,%)?
contributed by QandAEditors A subroutine may only know whether its caller wants
a SCALAR or an ARRAY. The wantarray function
handles this.
sub test {
if (wantarray){
return 'One String';
} else {
return ('A', 'List', 'of', 'Strings');
}
}
There is no built-in way to tell if a subroutine's
caller wants a hash, but davorg has posted a
sample of how you would do this (see
his answer).
The DBI module uses a similar technique
(non-relevant code removed for brevity):
sub fetchall_arrayref {
my $slice= shift || [];
my $mode = ref $slice;
if ($mode eq 'ARRAY') {
push @rows, [ @$row ] while($row = $sth->fetch);
}
elsif ($mode eq 'HASH') {
push @rows, $row while ($row = $sth->fetchrow_hashref);
}
else {
Carp::croak("fetchall_arrayref($mode) invalid")
}
return \@rows;
}
If you call fetchall_arrayref with an
array reference (or no reference), it will return
array references. If you call it with a hash
reference, it will return hash references.
$sth->fetchall_arrayref( [] ) # returns Array references
$sth->fetchall_arrayref( {} ) # returns Hash references
Cool stuff!
Russ
|
Please (register and) log in if you wish to add an answer
Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
Read Where should I post X? if you're not absolutely sure you're posting in the right place.
Please read these before you post! —
Posts may use any of the Perl Monks Approved HTML tags:
- a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
| |
For: |
|
Use: |
| & | | & |
| < | | < |
| > | | > |
| [ | | [ |
| ] | | ] |
Link using PerlMonks shortcuts! What shortcuts can I use for linking?
See Writeup Formatting Tips and other pages linked from there for more info.
|
|
