Hi Guys!

In my programm, I have a custom String-type that I want to initialize some variables of at compile time by casting a string literal to said custom String type. I thought I could achieve this straight forwardly, but after trying a bit, I could not find a (simple) working solution. I made this minimal example to show where the easy solution all fall flat:

struct My_String{
        long size;
        char* data;
}

My_String make_my_string(string s){
        My_String my_string;
        my_string.data = cast(char*) s.ptr;
        my_string.size = s.length;
        return my_string;
}

struct Dummy{
        My_String s = make_my_string("hello!");
}

void main(){
        Dummy dummy;
}

Which produces the compilation error "cannot use non-constant CTFE pointer in an initializer My_String(6L, &"hello!"[0])". I do not understand this error message. What is the non-constant CTFE pointer here. The "data"-member? If so, why does this compile:

struct My_String{
        long size;
        char* data;
}

struct Dummy{
My_String s = My_String("hello!".length, cast(char*) "hello!".ptr);
}

void main(){
        Dummy dummy;
}

Why does the error message show an opcall to My_String with filled out members ("6L, &"hello!"[0]"), although the code only ever default-constructs a My_string variable? I am confused. And why on earth does this work:

struct My_String{
        long size;
        char* data;
}

My_String make_my_string(string s){
        My_String my_string;
        my_string.data = cast(char*) s.ptr;
        my_string.size = s.length;
        return my_string;
}

void main(){
        My_String s = make_my_string("hello!");
}

Please help, I have no idea whats going on here.


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