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Subject: Re: [PHP-DEV] RFC: Traits for PHP
From: jochem@iamjochem.com (Jochem Maas)

Lars Strojny schreef:
> Hi Jochem,
> 
> Am Mittwoch, den 20.02.2008, 00:06 +0100 schrieb Jochem Maas:
> [...]
>> if a trait would could contain all the methods required to implement
>> an interface and a class uses it (the trait) and implements the
>> relevant interface would it (the interface) be satified?
> 
> Yes. The following should work:
> interface IFoo {
>    public function method();
> }
> 
> trait TFoo {
>    public functin method() {
>       echo "Hello World!";
>    }
> }
> 
> class CFoo implements IFoo
> {
>    use TFoo;
> }
> 
> This would be fine.
> 
>> also might it be an idea to allow a trait to specify that it
>> implements an interface for the purposes of development (errors
>> triggered due to incorrect/incomplete implementation)
>> BUT not have the interface be carried to any classes that use the
>> trait?
> 
> I don't see any sence in it. Why should one generalize an interface of a
> trait?

I don't suppose you would, I thinking more along the lines of having it
a developer tool - using implements on a trait would force the developer to
put in the correct methods, it might help a team that had say 1 interface, 2 traits
(which both contain a set of methods that satify said interface) and a large number
of classes that implement one or other of the traits ... having the trait state
that it's capable of handling an implementation might save some WTF because
compile time errors would happen on the trait if it broke the interface signature,
rather than on the class ... an interface related error on the class it might not be
obvious to the developer with regard to the fact that the/a trait the class is using
was for the purpose of satifying an interface the class states it is implementing.

I'm thinking that it will proably occur quite often that a fairly simple interface
will be 'covered' by a trait and that said trait would be used solely for satifying
said interface implementation and used as such for classes that wish to implement
said interface.

to quote Troels:

"Class inheritance (The ``extends`` keyword) inherits type
+ implementation. Interface inheritance (The ``implements`` keyword)
inherits type (but not implementation). Traits fill the missing hole
by allowing inheritance of implementation, but not type."

that sounds more than reasonable, but it might be worth offering an aid
to developers during the compile time phase, with regard to the 'link' between
a trait and an interface (assuming you would agree that it's not unlikely that
the two would be used in tandem on occasion) without imposing/implying anything
at run time (i.e. a trait may implement an interface to ensure correctness but
that has no effect on any class that uses it, classes must explicitly state it's
intention to implement an interface)

I may have said something stupid - but given the ability of your average php user
to stupid things with the functionality offered to him/her, my comments might
aid in thrashing out such details in order to limit a user's ability to do stupid
things :-)

> 
> cu, Lars