• MicroWizard (86/86) Feb 07 2006 What should 'writefln(var)' call when 'var' is interface?

MicroWizard <MicroWizard_member pathlink.com> writes:

What should 'writefln(var)' call when 'var' is interface?
What kind of 'toString' is called for interfaces?

If 'too few' methods are defined, then result is Access Violation,
which is sane.
If 'enough' methods are defined, then D calls 'some' method or picks up 'some'
data.

Is it normal or is it a bug?

Tamás Nagy


import std.stdio;
import std.string;

interface StringAlike
{
char[] Display();
}

class MyString:StringAlike
{
char[] disp;
public:
this(char[] st)
{
disp=st.dup;
}
char[] Display()
{
return disp;
}
}

void main(char[][] arg)
{
MyString a=new MyString("Ali Baba");

writefln("a:",a);
writefln("a.Display:",a.Display);

StringAlike sa=a;

writefln("sa:",sa);
writefln("sa.Display:",sa.Display);
}

a:MyString
a.Display:Ali Baba
sa:Error: Access Violation

import std.stdio;
import std.string;

interface StringAlike
{
char[] Display();
char[] Compare();
}

class MyString:StringAlike
{
char[] disp;
char[] comp;
public:
this(char[] st)
{
disp=st.dup;
comp=toupper(st);
}
char[] Display()
{
return disp;
}
char[] Compare()
{
return comp;
}
}

void main(char[][] arg)
{
MyString a=new MyString("Ali Baba");

writefln("a:",a);
writefln("a.Display:",a.Display);
writefln("a.Compare:",a.Compare);

StringAlike sa=a;

writefln("sa:",sa);
writefln("sa.Display:",sa.Display);
writefln("sa.Compare:",sa.Compare);
}

a:MyString
a.Display:Ali Baba
a.Compare:ALI BABA
sa:ALI BABA
sa.Display:Ali Baba
sa.Compare:ALI BABA