Default argument from member variable

[dlangBugzillaToGithub]

Luís Marques (@luismarques) reported this on 2013-04-25T19:54:34Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=9992

CC List

• yebblies

Description

In DMD64 v2.062, if you define a method with a default argument from a member variable, DMD only complains if the method is actually called:

    class Foo
    {
        int a = 0;

        void bar(int x = a)
        {
        }
    }

    void main()
    {
        Foo f = new Foo();
        //f.bar();   -> does not complain with this commented out
    }

With the method call it produces the error "need 'this' to access member a", which seems to be the defined behavior (but why not allow the default argument to be variable? you can just read 'a' and push it on the stack).

[dlangBugzillaToGithub]

yebblies commented on 2013-11-21T08:24:51Z

Default arguments are evaluated at the call site... so I don't think this is necessarily wrong.

[dlangBugzillaToGithub]

bearophile_hugs commented on 2013-11-21T08:31:01Z

(In reply to comment #1)
> Default arguments are evaluated at the call site... so I don't think this is
> necessarily wrong.

I think the compiler should give errors for wrong code, even if the function is not yet called.

[dlangBugzillaToGithub]

yebblies commented on 2013-11-21T08:43:23Z

Hmm, this doesn't work either.

class Foo
{
    int a = 0;

    void bar(int x = a)
    {
    }
    void baz()
    {
        bar();
    }
}

void main()
{
    Foo f = new Foo();
    //f.bar();   -> does not complain with this commented out
}

They probably should be banned.