[nem-en] usesite

[Vladimir Reshetnikov]

On 2/13/07, Kamil Skalski <kamil.skalski at gmail.com> wrote:
> It makes the created name bind to fields in class, breaking hygiene of
> macro generated expressions. This makes compiler look at the name as
> it was created plainly in contex of macro use-site.

I began to fix bug 892. I want to exclude null values from hashcode computation.
So, I changed macro in the following way:

  [Nemerle.MacroUsage (Nemerle.MacroPhase.WithTypedMembers,
                       Nemerle.MacroTargets.Class,
                       Inherited = false, AllowMultiple = false)]
  macro StructuralHashCode (t : TypeBuilder) {
    def flds = t.GetFields (BindingFlags.Public %|
BindingFlags.NonPublic %|
                            BindingFlags.Instance %| BindingFlags.DeclaredOnly);

    def body =
      List.FoldLeft (flds, <[ 0 ]>, fun (x : IField, acc) {
        <[ $acc %^ (if (object.ReferenceEquals($(x.Name : usesite),
null)) 0 else $(x.Name : usesite).GetHashCode ()) ]>
      });
    t.Define (<[ decl:
      public override GetHashCode () : int {
        $body
      }
    ]>);
  }

But this check for null makes sense only for reference types and
nullable value types. For non-nullale value types it is redundant. How
can I check in macro that target filed has a non-nullable value type?