Initialization in lazy function parameter allows immutable member not to be initialized

[dlangBugzillaToGithub]

David Eckardt reported this on 2013-06-28T09:00:44Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=10496

CC List

• Maxim Fomin
• Dicebot (@mihails-strasuns)

Description

class C
{
	immutable int x;
	
	this()
	{
		this.f(this.x = 5);
	}
	
	void f(lazy int x){}
}

C.int isn't initialized, although this code compiles.
Whether C.int is initialized or not depends on the, in general indeterministic, behavior of f(), this should be a compile time error.

[dlangBugzillaToGithub]

public (@mihails-strasuns) commented on 2013-06-28T09:21:47Z

I think this is part of a bigger problem:

----------------------------------------
class A
{
    immutable int x;

    void delegate() f;

    this()
    {
        x = 40;
        f = () { x = 42; };
    }
}

void main()
{
    import std.stdio;
    auto a = new A();
    writeln(a.x);
    a.f();
    writeln(a.x);
}
----------------------------------------

40
42

[dlangBugzillaToGithub]

maxim commented on 2013-06-28T11:08:00Z

The root is that delegate construction does not respect immutability at all.

struct S
{
   void foo() immutable {}
   void baz() 
   {
      //foo();
      (&foo)();
   }
}