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Date: Sun, 18 Sep 2022 16:21:02 +0430
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Subject: Specify abstract parent methods for traits
From: machitgarhaa@gmail.com (Mohammad Amin Chitgarha)

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Hi.

Currently, it's possible that, inside a trait's function, use the parent =
method of a class using the trait. This way, not only it's implicitly sup=
posed the trait is used in a class having a parent, but also the parent c=
lass has such a method. It doesn't seem to be a good practice, as stated =
in the answers of this question (https://softwareengineering.stackexchang=
e.com/questions/371067/should-a-trait-refer-to-parent-methods).
Also, it's almost impossible to override a parent method (using the same =
signature) using a trait. This is useful if you have to inherit multiple =
classes from a base class, but also override one (or more) of the base me=
thods with a common functionality provided by a trait.
There are some workarounds to these problems (specially talking about the=
 later one), but they have their own disadvantages:
Define a trait function with the same signature but a different name and =
use it. The main disadvantage is that it's a different method, and is not=
 polymorphic.
Do (1), include the trait in the derived class(es), then override the par=
ent method in all derived classes and manually call the trait function. N=
ot perfect because you have to copy the same code for all derived classes=
.

Stick with parent:: in the trait function. Implicit and not good (e.g. st=
atic analyzers and IDEs cannot help).

Change the parent class to use traits. This is not always possible, as it=
 might be someone else's code.

Ignore this please: copy and paste the method all over the place.

It's also not possible to use things like insteadof or as when including =
the trait.

Here, I want to propose the concept of explicitly declaring the parent me=
thod. The way to achieve this is to use attributes for trait functions, e=
.g. =23=5BOverride=5D.
It has the advantage of not requiring the redeclaration of the parent met=
hod as abstract. However, it should be not allowed to use as clause when =
including the trait function, as it's against the definition of overridin=
g a method (i.e. it must have the same name and visibility).
Another method is using a new parent specifier (i.e. abstract parent publ=
ic function =E2=80=A6), and is more (=3F) consistent with the current beh=
aviour. However, it requires duplicating the parent method signature.
There could be methods using insteadof or as, but they has nothing to do =
with the trait itself, and doesn't fix the problem of implicit declaratio=
n of the parent method in the trait.
Thanks,
Mohammad Amin Chitgarha.

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