[nem-bug] [Nemerle 0000805]: Does not report inability to infer type arguments

[feedback at nemerle.org]

A NOTE has been added to this issue.
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<http://nemerle.org/bugs/view.php?id=805> 
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Reported By:                Evin Robertson
Assigned To:                
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Project:                    Nemerle
Issue ID:                   805
Category:                   Compiler (type engine)
Reproducibility:            always
Severity:                   minor
Priority:                   normal
Status:                     new
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Date Submitted:             12-08-2006 23:04 CET
Last Modified:              12-08-2006 23:41 CET
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Summary:                    Does not report inability to infer type arguments
Description: 
The following code prints "false" because nemerle is unable to infer the
type parameter to F, making the call A.F.[object](y).  gmcs rejects the
equivalent C# program.  I think nemerle should do the same.  Attached is a
patch to implement an error, which may or may not be in the right place.

public class X
{
}

public class Y['t] : X
{
}


public module A
{
    public F['t](x : X) : bool
    {
	x is Y['t];
    }

    public Main() : void
    {
        def y = Y() : Y[int];
        def isY = A.F(y).ToString();
        System.Console.WriteLine(isY);
    }
}


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----------------------------------------------------------------------
 nazgul - 12-08-06 23:41 
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Oh, this is quite controversial request. I usually like this feature,
because it allows me to use any generic objects and methods without really
caring if types were inferred to something specific. 

For example I do:

def x = Hashtable ();
x.Add ("aaa", null);
x.Add ("bbb", null);
when (x.Contains (ReadLine()))
  WriteLine ("Got it");

and the second generic parameter is not important for me.

My rule of thumb is "if parameters were not inferred, then they are not
important - neither input arguments nor return type make any use of
them".

Of course I also see that if you use many type-checks on generic arguments
you would probably like compiler to prevent you having a bit "undefined"
behavior of your code.

Issue History
Date Modified  Username       Field                    Change              
======================================================================
12-08-06 23:04 Evin Robertson New Issue                                    
12-08-06 23:04 Evin Robertson File Added: CannotInfer.patch                    
12-08-06 23:41 nazgul         Note Added: 0001571                          
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