Do I understand correctly that in order for me to pass a string when creating an object, I must pass it by value? And if I have a variable containing a string, can I pass it by reference?

Should I always do constructor overloading for a type and a reference to it?
In the case of the variable c, a drop occurs. Why? An object is not being created on the stack?

import std.stdio : writeln;

class A
{
    private string str = "base";

    this(ref string str)
    {
        writeln("type reference string");
        this.str = str;
    }

    this(string str)
    {
        writeln("type string");
        this.str = str;
    }

    this() {}

    void print()
    {
        writeln(str);
    }
}

void main()
{
    auto a = new A("Hello, World!"); // this type string
    a.print();
    string text = "New string";
    auto b = new A(text); // this type reference string
    b.print();
    A c;
    c.print();  // segmentation fault! Why not "base"?
}

On Tuesday, 8 November 2022 at 12:30:50 UTC, Alexander Zhirov wrote:

A c;

this declaration not creates class instance. you should use "new".

btw, struct have other behavoiur

On Tuesday, 8 November 2022 at 12:30:50 UTC, Alexander Zhirov wrote:

import std.stdio : writeln;

class A
{
    private string str = "base";

    this(ref string str)
    {
        writeln("type reference string");
        this.str = str;
    }

    this(string str)
    {
        writeln("type string");
        this.str = str;
    }

    this() {}

    void print()
    {
        writeln(str);
    }
}

void main()
{
    auto a = new A("Hello, World!"); // this type string
    a.print();
    string text = "New string";
    auto b = new A(text); // this type reference string
    b.print();
    A c;
    c.print();  // segmentation fault! Why not "base"?
}

You forgot to assign "c" to anything, I think you meant:
A c = b;
Read that segmentation fault as null pointer exception.

Whenever you assign something to ref type something, it will basically be the same as writing myVariable = *something; in C code, so, in that case, it won't make any difference.

The `ref` attribute only means that if you change your string inside the code that takes by ref, it will reflect when returning, such as:
```d
void modifyString(ref string input)
{
   input~= "Now it is modified";
}
string text = "New string";
modifyString(text);
writeln(text); //"New stringNow it is modified"
```

Thanks for answers!

On Tuesday, 8 November 2022 at 12:43:47 UTC, Adam D Ruppe wrote:

So it's always working with thick pointers?

If I create just A c, then is it an empty pointer?

On Tuesday, 8 November 2022 at 13:05:09 UTC, Ali Çehreli wrote:

Thanks! 🙂