Re: struct constructor with rvalue param of same struct type

[vit via Digitalmars-d-learn]

On Tuesday, 19 January 2021 at 06:49:06 UTC, Kyle Ingraham wrote:
I’m sorry that this isn’t a solution to your problem but your 
code caught my attention. What is your snippet supposed to do?

This is more specific example:
https://run.dlang.io/is/W7rd2u

import std.traits : CopyTypeQualifiers;

struct Ptr(T)
if(is(T == struct)){
    private void* ptr;

    static if(is(T == const))
    this(ref const typeof(this) x)@trusted{
        this.ptr = cast(typeof(this.ptr))x.ptr;
    }

    this(ref typeof(this) x)@safe{
        this.ptr = x.ptr;
    }

    this(ref const typeof(this) x)const @safe{
        this.ptr = x.ptr;
    }

    this(P : const Ptr!(U), U, this This)(auto ref P x)@trusted
    if(true
        //&& !is(R == T)
        && is(CopyTypeQualifiers!(P, U)* : 
CopyTypeQualifiers!(This, T)*)
    ){
        this.ptr = cast(typeof(this.ptr))x.ptr;
    }

}


struct Foo{
    //@disable this(this);
}

T get_rvalue(T)(){              
        return T.init;
}

void main()@safe{

    ///normal pointers
    {
        const(const(Foo)*) cpcf;        ///const(Foo*)

        const(Foo*) cpf1 = cpcf;                                ///OK   
        const(Foo*) cpf2 = get_rvalue!(const(const(Foo)*));     ///OK   

        const(Foo)* pcf1 = cpcf;                                ///OK   
        const(Foo)* pcf2 = const(const(Foo)*).init;             ///OK
        const(Foo)* pcf3 = get_rvalue!(const(const(Foo)*));     ///OK

    }

    //wrapped ptr:
    {
        const Ptr!(const Foo) cpcf;

        const Ptr!(Foo) cpf1 = cpcf;                                    ///OK
        const Ptr!(Foo) cpf2 =  get_rvalue!(const Ptr!(const 
Foo));	///OK

        Ptr!(const Foo) pcf1 = cpcf;                                    ///OK
        Ptr!(const Foo) pcf2 = const(Ptr!(const Foo)).init;             ///OK
        Ptr!(const Foo) pcf3 = get_rvalue!(const Ptr!(const 
Foo));	///ERROR!
    }
}