~= call copy ctor?

[Namespace]

I have a 2 questions.

I have this code:

[code]
import std.stdio;

struct Test {
public:
	this(int i = 0) {
		writeln("Test CTor.");
	}

	this(this) {
		writeln("Test Copy CTor");
	}

	~this() {
		writeln("Test DTor");
	}
}

Test[] _arr;

void copy_save(Test t) {
	_arr ~= t;
}

void by_ref_save(ref Test t) {
	_arr ~= t;
}

[/code]

Why get i with

[code]
void main() {
	Test t = 42;

	by_ref_save(t);
}
[/code]

this output:

Test CTor.
Test Copy CTor
Test DTor

?

Why t is copied?

And the same if i have this:

[code]
void main() {
	Test t = 42;

	copy_save(t);
}
[/code]

t is already a clone. Why it is copied again?

Thanks in advance. :)