• 60rntogo (35/35) Sep 13 2020 This code:
• Adam D. Ruppe (25/28) Sep 13 2020 You can override members from mixin templates by giving a member
• 60rntogo (2/6) Sep 13 2020 Yes, that works. Thanks!

60rntogo <60rntogo gmail.com> writes:

This code:

---
mixin template X()
{
   int[2] x;

   this(int[2] x...)
   {
     this.x = x;
   }
}

struct Foo
{
}

struct Bar
{
   mixin X;

   this(Foo foo)
   {
     this.x = [0, 0];
   }
}

void main()
{
   auto bar = Bar(1, 2);
}
---

produces the following error:

---
source/app.d(27,17): Error: constructor app.Bar.this(Foo foo) is 
not callable using argument types (int, int)
source/app.d(27,17):        cannot pass argument 1 of type int to 
parameter Foo foo
---

However, if I directly insert the contents of X into Bar instead 
of mixing it in, it compiles just fine. What's going on here?

Adam D. Ruppe <destructionator gmail.com> writes:

On Sunday, 13 September 2020 at 12:34:06 UTC, 60rntogo wrote:
 However, if I directly insert the contents of X into Bar 
 instead of mixing it in, it compiles just fine. What's going on 
 here?

You can override members from mixin templates by giving a member 
with the same *name* (not the same signature!) directly.

mixin template foo() { int a; }

class Thing { mixin foo; string a; /* this a overrides foo's a */ 
}


This is pretty useful in a lot of cases but kinda annoying with 
overloading. To overload, you must use `alias` to merge the 
overload sets. For constructors, you need to use the name 
`__ctor` instead of `this` to make it compile:

```
struct Bar
{
   mixin X some_name; // notice the addition of a name

   this(Foo foo)
   {
     this.x = [0, 0];
   }

   alias __ctor = some_name.__ctor; // merge the overloads
}
```

Read more here:

http://dpldocs.info/this-week-in-d/Blog.Posted_2020_01_20.html#understanding-mixin-templates

and here too:

https://stackoverflow.com/a/57712459/1457000

60rntogo <60rntogo gmail.com> writes:

On Sunday, 13 September 2020 at 13:10:15 UTC, Adam D. Ruppe wrote:
 This is pretty useful in a lot of cases but kinda annoying with 
 overloading. To overload, you must use `alias` to merge the 
 overload sets. For constructors, you need to use the name 
 `__ctor` instead of `this` to make it compile:

Yes, that works. Thanks!