public static Expression ImplicitTypeParameterConversion (Expression expr, TypeParameterSpec expr_type, TypeSpec target_type)
{
//
// From T to a type parameter U, provided T depends on U
//
if (target_type.IsGenericParameter) {
if (expr_type.TypeArguments != null && expr_type.HasDependencyOn (target_type)) {
if (expr == null)
return EmptyExpression.Null;
if (expr_type.IsReferenceType && !((TypeParameterSpec) target_type).IsReferenceType)
return new BoxedCast (expr, target_type);
return new ClassCast (expr, target_type);
}
return null;
}
//
// LAMESPEC: From T to dynamic type because it's like T to object
//
if (target_type.BuiltinType == BuiltinTypeSpec.Type.Dynamic) {
if (expr == null)
return EmptyExpression.Null;
if (expr_type.IsReferenceType)
return new ClassCast (expr, target_type);
return new BoxedCast (expr, target_type);
}
//
// From T to its effective base class C
// From T to any base class of C (it cannot contain dynamic or be of dynamic type)
// From T to any interface implemented by C
//
var base_type = expr_type.GetEffectiveBase ();
if (base_type == target_type || TypeSpec.IsBaseClass (base_type, target_type, false) || base_type.ImplementsInterface (target_type, true)) {
if (expr == null)
return EmptyExpression.Null;
if (expr_type.IsReferenceType)
return new ClassCast (expr, target_type);
return new BoxedCast (expr, target_type);
}
if (target_type.IsInterface && expr_type.IsConvertibleToInterface (target_type)) {
if (expr == null)
return EmptyExpression.Null;
if (expr_type.IsReferenceType)
return new ClassCast (expr, target_type);
return new BoxedCast (expr, target_type);
}
return null;
}
static Expression ExplicitTypeParameterConversionToT (Expression source, TypeSpec source_type, TypeParameterSpec target_type)
{
//
// From the effective base class C of T to T and from any base class of C to T
//
var effective = target_type.GetEffectiveBase ();
if (TypeSpecComparer.IsEqual (effective, source_type) || TypeSpec.IsBaseClass (effective, source_type, false))
return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
return null;
}
