On 10/02/2021 21:17, Ryan Joseph via fpc-pascal wrote:
On Feb 10, 2021, at 12:40 PM, Martin Frb via fpc-pascal
<fpc-pascal@lists.freepascal.org> wrote:
type
TSomeTrait = trait
public
procedure DoTraitFoo;
end;
TSomeClass = class(TObject)
private
trait: TSomeTrait; // whatever syntax is used so that the trait is added
public
SomeVal: Integer;
procedure DoSome;
procedure Dispatch(var message); override;
end;
if it's the simple then just set a reference to TSomeClass inside of
TSomeTrait. If the trait doesn't know anything about the implementor then you
indeed need to use a dispatch table or something. Can't this be solved with
existing features?
btw, I don't think we should model this based on PHP, I just gave that as an
example. The Swift model is much more simple and does 99% of what you want. I
think that's what we should do for Pascal also.
I don't have a pro/contra agenda on whether that feature should be part
of the fpc trait or not.
I just saw it, and thought I raise it.
But also, if any option should be reserved for the future, then it
matters. Because re-using "sometrait = object end" makes it less likely
that an "implements" clause will be added (because "object" does already
have a fully defined syntax).
So I felled it might be worth being noted.
------
Another option would be
TSomeTrait = trait (basetrait) for (someclass_as_minimum_base_class)
for (someclass) is of course optional (or rather default to TObject).
So sometrait then can access
self.any_trait_identifier
self.someclass_ident
This is a bit limiting at first, but bring in genericts
generic TSomeTrait = trait (basetrait) for (<T>)
Since it is a generic the compiler will not complain about unknown
identifiers.
It can automatically specialise, when applying a trait.
Then again the "implements" clause from above could internally create a
generic too.
----------------------
Btw, next question that just came up
Will traits only apply to classes?
or could a record / advanced record / old object also receive traits ?
------------------------
And one more thing that may at least be considered for design in case of
future use.
Consider a Trait
TEmployeList = trait
function FindByUnallocateWorkTime: TEmploye;
end;
TCompany = class
end;
Now the company could have Engineers and Designers. It needs to lists....
But the trait can obviously only be added once.
Yet no-one wants to copy and paste the trait to create a 2nd verson
Maybe Something like
TDesignerList = trait(TEmployeList)
function FindDesigerByUnallocateWorkTime: TEmploye; aliases
FindByUnallocateWorkTime;
end;
--------------
Again, none of those are needed. But if they are found interesting....
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