On 09/03/2017 08:54 PM, Eric_DD wrote:
*** This works:
struct Array {
void foo() { writeln("foo"); }
}
mixin template arrayOperations(arrays...) {
void foo() {
foreach(ref a; arrays) a.foo();
}
}
class Thing {
Array data1;
Array data2;
mixin arrayOperations!(data1, data2);
}
[...]
***
But if I wrap Array in a S, then I get a "need this for data of type Array"
Is there a way (without an alias this in S) to get the following working?
*** Non working code:
[...]
struct S {
Array data;
}
[...]
class Thing {
S s1;
S s2;
mixin arrayOperations!(s1.data, s2.data);
}
As far as I understand, the problem is that an alias of a member does
not carry a `this` reference. It's added only when you use the alias in
a method of the aggregate.
That means, s1.data is not an alias of s1's `data` field, but an alias
of `S.data`. And so is `s2.data`. They're effectively the same alias.
It's the same with `data1` and `data2`. But in that case the aliases
work because `foo` provides the correct `this` reference.
An example of what I mean:
----
import std.stdio;
class C
{
int field;
void method() { writeln(f); }
}
C c1;
C c2;
alias f = c1.field;
void main()
{
c1 = new C;
c2 = new C;
c1.field = 1;
c2.field = 2;
c1.method(); /* prints "1" */
c2.method(); /* prints "2" */
version (none) writeln(f); /* Error: need 'this' */
}
----
Note that `c2.method()` prints "2", even though the alias f has been
made from c1. The alias doesn't refer to c1's specific field, but to the
generic field of the C class. The alias can only be used in methods of
C, because they provide the needed `this`.
