[nem-bug] [Nemerle 0000832]: comparing structs with == raises error

[feedback at nemerle.org]

The following issue has been RESOLVED.
======================================================================
<http://nemerle.org/bugs/view.php?id=832> 
======================================================================
Reported By:                Luntain
Assigned To:                nazgul
======================================================================
Project:                    Nemerle
Issue ID:                   832
Category:                   Code Completion Engine
Reproducibility:            always
Severity:                   minor
Priority:                   normal
Status:                     resolved
Resolution:                 not an issue
Fixed in Version:           
======================================================================
Date Submitted:             01-21-2007 11:19 CET
Last Modified:              01-26-2007 19:36 CET
======================================================================
Summary:                    comparing structs with == raises error
Description: 
[Record] public struct Point
   x: double
   y: double

...

def p = Point(0,0)
def q = Point(0,0)
assert p==q //merror&http://nemerle.org/bugs/view.php?id=8592;[0m: comparing
values of types Point and Point
with reference equality
======================================================================

----------------------------------------------------------------------
 nazgul - 01-22-07 17:51 
----------------------------------------------------------------------
Right... you need to provide the comparison operator:


[Record]
struct P {
   public x : int;
   
   public static @== (a : P, b : P) : bool {
     a.x == b.x   
   }
}

def a = P (1);
def b = P (1);
System.Console.WriteLine (a == b);


I don't think that any "magic" implementation of such comparison operators
would be desired (especially by default). Even if it would be done by
shallow comparison of fields - there could be still some reference fields
in given struct and comparing them by reference is quite bug prone.

Note, that .NET gives you this feature when you use Equals method:

[Record]
struct P {
   public x : int;
}

def a = P (1);
def b = P (1);
System.Console.WriteLine (a.Equals (b));


and our approach is to actually forbid using ANY == unless types has
explicit == operator defined or user upcast to object.

----------------------------------------------------------------------
 nazgul - 01-26-07 19:36 
----------------------------------------------------------------------
By design.

Issue History
Date Modified  Username       Field                    Change              
======================================================================
01-21-07 11:19 Luntain        New Issue                                    
01-22-07 17:51 nazgul         Note Added: 0001631                          
01-22-07 17:51 nazgul         Status                   new => feedback     
01-22-07 17:51 nazgul         Description Updated                          
01-26-07 19:36 nazgul         Status                   feedback => resolved
01-26-07 19:36 nazgul         Resolution               open => not an issue
01-26-07 19:36 nazgul         Assigned To               => nazgul          
01-26-07 19:36 nazgul         Note Added: 0001645                          
======================================================================