Any reason why "(ref $class || $class)" is deprecated?

It can make the semantics of your constuctor confusing. If I want a new object of class Foo then I want to call Foo->new. I'd probably expect $foo->new to clone $foo, but if the class author wanted that functionality they should have created an object method called "clone" or something like that.

In general, it's a good idea to have class methods and object methods completely separate from each other. The ref $class || $class idiom breaks that distinction.

It is useful if you want a new instance based on the same class as an existing object, without having to hard-code the class name.

Well, you can always use (ref $foo)->new if that's what you want.

I'd probably expect $foo->new to clone $foo, but if the class author wanted that functionality they should have created an object method called "clone" or something like that.

That, I do not understand. If you expect the author to name clone functionality clone, then why assume that new clones the object?

I'd expect something called new to give me a new thing - not a cloned one.

Well, you can always use (ref $foo)->new if that's what you want.

That's not much of an argument, is it? With such an argument, we could do away with for/foreach, unless, and/or, q/qq/qw/qx, etc. There are always alternatives taking a few more keystrokes.

And note that the existance of ref $proto || $proto in a constructor doesn't prevent you from writing:

    (ref $foo)->new
[download]

if

    $foo->new
[download]

confuses you.

But the absense of ref $proto || $proto forces someone who doesn't confuse easily to write:

    (ref $foo)->new
[download]

Ergo, using ref $proto || $proto gives the user of the module more choice.

My point was that $foo->new has confusing semantics. It should mean something like "create a new object based on $foo" not "create a new object of the same class as $foo". Who knows whether $foo->new creates a new, empty object of the same class or a complete copy of $foo. It's not clear unless you read the docs or the source code. I didn't say that I was confused, just that it was potentially confusing :)

Good OO programming practice is that class methods and object methods should be distinct. I think that it's a shame that common Perl practice seems to be to ignore that practice as it makes OO programming in Perl seem more complex than it needs to be.

--
<http://www.dave.org.uk>

"The first rule of Perl club is you do not talk about Perl club."
-- Chip Salzenberg

The existance of

    ref $proto || $proto
[download]

in the constructor doesn't prevent you from using new strictly as a class method.

It just doesn't enforce that upon someone who doesn't mind.

I use

    ref $proto || $proto
[download]

in my constructors, but I use my constructors purely as class methods. However, I let other uses of my modules free in their choice.

Writing ref $proto || $proto allows the caller of the constructor to create a new object by calling:

    $obj -> new;
[download]

I think that's silly. If something confuses you, don't use it. No need to jihad the thing that enables you to get confused.