non-constant expression while initializing two dim array

[Basile B.]

On Monday, 8 June 2020 at 06:37:18 UTC, tirithen wrote:
> How can I initialize my two dimensional array?
>
> When I try to run the code below I get the error:
>
>     Error: non-constant expression ["user":[cast(Capability)0], 
> "administrator":[cast(Capability)1]]
>
> Code:
>
>     enum Capability {
>       self,
>       administer
>     }
>
>     alias Capabilities = immutable Capability[];
>
>     private Capabilities[string] roleCapabilities = [
>       "user" : [Capability.self], "administrator" : 
> [Capability.administer]
>     ];
>
> I have tried adding more const and immutable prefixes but it 
> still gives me the same error. The goal is that 
> roleCapabilities should be an immutable/const two dimensional 
> array.

What you declare here is not a two dim array it's an associative 
array.
Associative array implementation have limitations. To initialize 
one that doesn't have const expr as key you can use a static 
module constructor:

---
enum Capability {
   self,
   administer
}

alias Capabilities = immutable Capability[];

private Capabilities[string] roleCapabilities;

static this()
{
     roleCapabilities = [
       "user" : [Capability.self], "administrator" : 
[Capability.administer]
     ];
}
---

which is done at runtime, just before the D main() get executed.

Notes:

1. You can also use a function containing a switch statement 
instead of an assoc array.
2. the other way would work because it would be a static array, 
the enum member giving an integer index:

---
enum Capability {
   self,
   administer
}

alias Capabilities = immutable Capability[];

private string[Capability.max + 1] roleCapabilities = [
     Capability.self : "user",
     Capability.administer : "administrator",
];
---

but I suppose that is different.