Error: cannot implicitly convert expression this.aa of type inout(string[string]) to string[string]

[Robert-D]

On Thursday, 15 March 2018 at 13:18:38 UTC, Simen Kjærås wrote:
> On Thursday, 15 March 2018 at 12:00:08 UTC, Robert-D wrote:
>> I want the function to create a mutable copy from a const or a 
>> imutable
>>
>> Like this:
>>
>> void main() {
>>     const S s = S(["": ""]);
>>     S b = s.dup();
>> }
>>
>> How can i do that?
>
> In that case, the problem is that you also have to .dup the aa:
>
>     S dup() const pure {
>         return S(aa.dup);
>     }
>
> However, it seems aa.dup returns the wrong type - one would 
> expect V[K] for inout(V[K]), but it returns inout(V)[K], or 
> inout(string)[string], in your case. That's apparently a known 
> bug: https://issues.dlang.org/show_bug.cgi?id=14148.
>
> The solution for now, then, is this:
>
>     S dup() const pure {
>         return S(cast(string[string])aa.dup);
>     }
>
> --
>   Simen

Why something like this doesn't compile (with or without the cast 
on bb.dup)?

struct S {
     string[string] aa;

     S dup() inout pure {
         return S(cast(string[string]) aa.dup);
     }
}

struct SS {
     S[] bb;

     SS dup() inout pure {
         return SS(cast(S[]) bb.dup);
     }
}


Error: static assert: "Cannot implicitly convert type inout(S) to 
S in dup."

Or:

const(S)[] ss = [S(["": ""])];
S[] d = ss.dup;

Error: template object.dup cannot deduce function from argument 
types !()(const(S)[]), candidates are:
/dlang/dmd/linux/bin64/../../src/druntime/import/object.d(2086):  
       object.dup(T : V[K], K, V)(T aa)
/dlang/dmd/linux/bin64/../../src/druntime/import/object.d(2122):  
       object.dup(T : V[K], K, V)(T* aa)
/dlang/dmd/linux/bin64/../../src/druntime/import/object.d(4191):  
       object.dup(T)(T[] a) if (!is(const(T) : T))
/dlang/dmd/linux/bin64/../../src/druntime/import/object.d(4207):  
       object.dup(T)(const(T)[] a) if (is(const(T) : T))