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Subject: Re: [PHP-DEV] Singletons
From: rowan.collins@gmail.com (Rowan Collins)

George Wilson wrote (on 05/02/2014):
> The point (at least in Java) is two fold- one is to separate behavior from
> implementation to achieve better separation of concerns
> [...]
> The other (which is really just an application of number one) is using them
> to group together different classes under a similar banner (again, in Java
> this is really a type issue). You could use this in cases where you do not
> want to define an abstract class for instance but still want some
> uniformity.

This sounds like a good description of why to use Interfaces in general, 
but doesn't really explain why it is the language's responsibility to 
define those interfaces for you, rather than some framework.

Obviously, there is a benefit to using the same Interfaces in multiple 
projects, and this is what groups like FIG are working on. A similar 
role in the Java world might be the various Apache Foundation groups 
working on interoperable tools, but not contributing to the Sun/Oracle 
JDK directly.

> I know a friend of mine up North is a big fan of traits which from what I
> can tell are basically an extension of interfaces (please correct me if I
> am wrong- I have not used them).

Traits are a slightly different concept, sometimes referred to as 
"horizontal reuse". They don't create any kind of inheritance 
relationship between two classes, just allow you to write some code once 
and use it in several places. Essentially, they are an automated 
copy-and-paste.

[PS: Please reply below, rather than above, other people's posts, 
preferably trimming the quote to the relevant part as I've done here.]

Regards,
-- 
Rowan Collins
[IMSoP]