Contributed by PsychoSpunk
on Jun 21, 2000 at 23:37 UTC
Q&A
> object-oriented programming
Description: I'm wanting to provide a bit of determinism to the
constructor method, and was wondering if I can simply make
sub new {
my $value1, $value2 = @_;
...
}
and
sub new {
my $only_value = shift;
... (not the same as above ...)
}
Am I looking for too much here? Or is there just no way to
really effectively pull this one off other than putting it
in one constructor that does the logic and passes off to
other subs based on the values it gets?
Thanx.
Mike Answer: How do I make deterministic constructors?
contributed by btrott You mean can you make your constructors prototyped
so that the correct constructor gets invoked
based on the number of parameters you provide,
like you might do in C++?
I don't think you can do this in Perl, because
Perl's version of prototypes isn't the same as
C++'s. Differently-prototyped subroutines with
the same name don't fly in Perl. I don't think.
My question would be: are you sure you need to
do this? Perhaps there's a better way of handling
this in Perl that doesn't require such a thing.
One way to do it would be to pass in the
parameters as a hash, then just dump that hash
into the hash-reference object that you create:
package R;
sub new {
my $this = shift;
my $class = ref($this) || $this;
my $self = { @_ };
bless $self, $class;
}
Now people can create a new R object
any way they please:
my $r1 = new R;
my $r2 = new R (foo => 'bar');
my $r3 = new R (baz => 'quux', foo => 'bar');
and so on. Would that work for you? | Answer: How do I make deterministic constructors?
contributed by Perlmage The short answer is: you can't. Perl doesn't
do multiple multiple dispatch.
The long answer is: Use the
Class::Multimethods
module. As is the case with many of the things
that "Perl doesn't do", Damian Conway has made
Perl do it.
| Answer: How do I make deterministic constructors?
contributed by herveus Howdy!
Consider:
sub new
{
if (@_ == 2) { new_1(@_); }
elsif (@_ == 1) { new_2(@_); }
else { warn "bad parameter..."; }
}
where subs new_1 and new_2 are your alternatives.
You can do more detailed checking of the characteristics of the contents of @_ as needed.
Of course, there is Class:Multimethods as mentioned earlier to automate this.
yours,
Michael | Answer: How do I make deterministic constructors?
contributed by QandAEditors While waiting for an answer, I've been playing
with a few ideas. I've touched on passing hashes
into the constructor, as well as lists. I guess I
was hoping that it could be done in what I view to
be a simplistic way instead of either handling
cases where I look for the existence of x to
determine which route to apply, or by having
multiple methods which are constructors (in the
sense that they bless) that follow no particular
naming convention. Thanks for the confirmation
that I wasn't overlooking something (I'm just now
dabbling in the black arts of Perl OO, and have
not yet purchased the OO Perl book). |
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!
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
Outside of code tags, you may need to use entities for some characters:
| |
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.
|
|
