Re: "this" as default parameter for a constructor.
On Sunday, 11 April 2021 at 20:38:10 UTC, Pierre wrote:
Hi,
I have a class with a reference to the parent object and a
constructor that has the parent as parameter
class foo {
this ( foo p /* , other params */ ) {
parent = p;
}
foo parent;
}
Of cause, the parent is almost always the object that creates
the new intance. So
auto f = new foo(this);
I'd like to set "this" ( the creator ) as default argument if
the constructor :
this ( foo p = this ) {...}
I can't. But however, the function, the argument and the
current object in body of the constructor are 3 different
things and the compiler can distinguish each one.
Is there a way to pass the reference of the caller to the
creator as default argument ?
Depending on what you are trying to do, I would recommend to
instead go with nested classes if you can. E.g.
```D
class MyClass {
class MyChild {
this (int value) { this.value = value; }
private int value;
}
}
void main ()
{
auto mc = new MyClass;
auto child = mc.new MyChild(42);
}
```
It'll give you an automatic reference to the parent. Of course if
you are trying to do something like linked list, where all
elements have the same type, it won't work.
In this case, the `create` approach might be better. You should
be able to cook something with a template `this` parameter to
reduce boilerplate.
And regarding allowing `this` as default argument: Definitely no.
While it could be possible with some stretch (e.g. we'll have to
delay default parameter semantic to the call site, unlike what is
currently done, and that would mess with things like overload
resolutions and template type inference), it wouldn't be sound /
it'd be very surprising. I for one would expect `this` to be the
object referencing itself, not the `this` of my caller.
Re: "this" as default parameter for a constructor.
On Monday, 12 April 2021 at 13:14:27 UTC, Kagamin wrote:
class foo {
this ( foo p /* , other params */ ) {
parent = p;
}
foo create() {
return new foo(this);
}
void use() {
foo f = create();
}
foo parent;
}
It's a solution. But my foo class is a base for several
subclasses which each have their own constructor with different
parameters; i should define as much create function as subclasses
constructors. that's unelegant. I tried do solve it with
templates but couldn't found a satisfatory solution.
As @Jack say " this ( T p = this ){...} " if not supported, not
yet, maybe it should be ?
By now, the "best" way i found is to write auto f = new foo(this);
Re: "this" as default parameter for a constructor.
On Sunday, 11 April 2021 at 20:38:10 UTC, Pierre wrote:
Hi,
I have a class with a reference to the parent object and a
constructor that has the parent as parameter
class foo {
this ( foo p /* , other params */ ) {
parent = p;
}
foo parent;
}
Of cause, the parent is almost always the object that creates
the new intance. So
auto f = new foo(this);
I'd like to set "this" ( the creator ) as default argument if
the constructor :
this ( foo p = this ) {...}
I can't. But however, the function, the argument and the
current object in body of the constructor are 3 different
things and the compiler can distinguish each one.
Is there a way to pass the reference of the caller to the
creator as default argument ?
it isn't supported as far i know so use a default construtor like
@Kagamin has show
Re: "this" as default parameter for a constructor.
class foo {
this ( foo p /* , other params */ ) {
parent = p;
}
foo create() {
return new foo(this);
}
void use() {
foo f = create();
}
foo parent;
}
"this" as default parameter for a constructor.
Hi,
I have a class with a reference to the parent object and a
constructor that has the parent as parameter
class foo {
this ( foo p /* , other params */ ) {
parent = p;
}
foo parent;
}
Of cause, the parent is almost always the object that creates the
new intance. So
auto f = new foo(this);
I'd like to set "this" ( the creator ) as default argument if the
constructor :
this ( foo p = this ) {...}
I can't. But however, the function, the argument and the current
object in body of the constructor are 3 different things and the
compiler can distinguish each one.
Is there a way to pass the reference of the caller to the creator
as default argument ?
