• Bradley Smith <digitalmars-com baysmith.com> Jan 14 2007
• Charles D Hixson <charleshixsn earthlink.net> Feb 03 2007

Bradley Smith <digitalmars-com baysmith.com> writes:

import std.stdio;

class A {
   this(float v) { value = v; }
   float getValue() { return value; }
	
private:
   float value;
}

typedef A B;

void main() {
   B b = new B(1);
   writefln(b.value);
}

The above code produces the following errors:
dmd testTypedef.d


B(1F)) of type testTypedef.A to B
testTypedef.d(15): Error: this for value needs to be type A not type B

Aliasing works for classes, but not typedef. Why not?

Thanks,
   Bradley

Charles D Hixson <charleshixsn earthlink.net> writes:

Bradley Smith wrote:
 
 import std.stdio;
 
 class A {
   this(float v) { value = v; }
   float getValue() { return value; }
     
 private:
   float value;
 }
 
 typedef A B;
 
 void main() {
   B b = new B(1);
   writefln(b.value);
 }
 
 The above code produces the following errors:
  >dmd testTypedef.d
 testTypedef.d(14): Error: cannot implicitly convert expression (new 
 B(1F)) of type testTypedef.A to B
 testTypedef.d(15): Error: this for value needs to be type A not type B
 
 Aliasing works for classes, but not typedef. Why not?
 
 Thanks,
   Bradley


(Seems, not is.)  I don't have a small example but I defined
typedef	uint	NodeNbr;
typedef	NodeNbr	ObjAddr;

and then got:
charles mandala1:~/projects/D/Parody$ dmd -c db.d
db.d(37): constructor node.Node.this (NodeFile,NodeNbr) does 
not match parameter types (NodeFile,uint)
db.d(37): Error: cannot implicitly convert expression (n) of 
type uint to NodeNbr
charles mandala1:~/projects/D/Parody$ dmd -c db.d
db.d(37): constructor node.Node.this (NodeFile,NodeNbr) does 
not match parameter types (NodeFile,NodeNbr)
db.d(37): Error: cannot implicitly convert expression (n) of 
type NodeNbr to NodeNbr
charles mandala1:~/projects/D/Parody$ dmd -c db.d
db.d(37): constructor node.Node.this (NodeFile,NodeNbr) does 
not match parameter types (NodeFile,NodeNbr)
db.d(37): Error: cannot implicitly convert expression (nd) of 
type NodeNbr to NodeNbr

(Each separate compilation represents a different way of 
arranging things.)

FWIW, they were calling a class defined in another file, and I 
got around this by using:
typedef	node.NodeNbr	ObjAddr;

This does make sense.  But the error message is so totally 
unhelpful that this almost doesn't seem worth the effort.

When I used alias instead of typedef it compiled without 
error.  That was the first step in figuring out what the 
problem was.  Better error messages are REALLY needed!