Hi,

I'm trying to do something similar to what Kotlin allows with assigning to member variables from a map. The syntax is very readable and looks like:

class User(val map: Map<String, Any?>) {
    val name: String by map
    val age: Int     by map
}

So I'm trying to do something similar in D:

mixin template MapMembers(alias aa) {
  foreach (name; typeof(this).tupleof) {
    // if name is in aa, then mixin(m = aa[" ~ m ~ "]) ... ish
  }
}
struct User {
  this(Variant[string] aa) {
    mixin MapMembers!aa;
  }
}

Seems I can't do typeof(this) inside the mixin.

One workaround is to explicitly pass the type "User" to the template mixin, but it feels like this is something that should work and I'm just unfamiliar with template mixins and their usage.

Cheers,
- Ali

[0] https://kotlinlang.org/docs/reference/delegated-properties.html#storing-properties-in-a-map

On Tuesday, 28 August 2018 at 20:39:16 UTC, aliak wrote:
> Hi,
>
> I'm trying to do something similar to what Kotlin allows with assigning to member variables from a map. The syntax is very readable and looks like:
>
> class User(val map: Map<String, Any?>) {
>     val name: String by map
>     val age: Int     by map
> }
>
> So I'm trying to do something similar in D:
>
> mixin template MapMembers(alias aa) {
>   foreach (name; typeof(this).tupleof) {
>     // if name is in aa, then mixin(m = aa[" ~ m ~ "]) ... ish
>   }
> }
> struct User {
>   this(Variant[string] aa) {
>     mixin MapMembers!aa;
>   }
> }
>
> Seems I can't do typeof(this) inside the mixin.
>
> One workaround is to explicitly pass the type "User" to the template mixin, but it feels like this is something that should work and I'm just unfamiliar with template mixins and their usage.
>
> Cheers,
> - Ali
>
> [0] https://kotlinlang.org/docs/reference/delegated-properties.html#storing-properties-in-a-map

Isn't the problem, that inside a template a declaration is expected, and not a foreach?

This works as expected:

´´´
import std.experimental.all;

void main()
{
	writeln("Edit source/app.d to start your project.");
}
mixin template MapMembers(alias aa) {
	typeof(this) var;
	/*
  foreach (name; typeof(this).tupleof) {
    // if name is in aa, then mixin(m = aa[" ~ m ~ "]) ... ish
  }
	*/
}
struct User {
  this(Variant[string] aa) {
    mixin MapMembers!aa;
  }
}
//mixin MapMembers!(Variant[string].init);
´´´

On Tuesday, 28 August 2018 at 20:58:23 UTC, Alex wrote:
>
> Isn't the problem, that inside a template a declaration is expected, and not a foreach?
>


Boh, you're right. I guess I misunderstood mixin templates. Found a way with a normap function though :p

void mapSelf(alias self, alias aa)() { ... }

this(map) {
   mapSelf!(this, map);
}

https://run.dlang.io/is/EhDpOM