[Mono-bugs] [Bug 543570] New: CS0425 on generic method with T constrained to struct and return value is nullable (T?)

[bugzilla_noreply at novell.com]

http://bugzilla.novell.com/show_bug.cgi?id=543570


           Summary: CS0425 on generic method with T constrained to struct
                    and return value is nullable (T?)
    Classification: Mono
           Product: Mono: Compilers
           Version: 2.4.x
          Platform: Other
        OS/Version: All
            Status: NEW
          Severity: Critical
          Priority: P5 - None
         Component: C#
        AssignedTo: mono-bugs at lists.ximian.com
        ReportedBy: arnec at mindtouch.com
         QAContact: mono-bugs at lists.ximian.com
          Found By: ---


User-Agent:       Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US;
rv:1.9.1) Gecko/20090624 Firefox/3.5

With an interface with a generic method of value T, returning T?, where T is
constrained to a struct, the implementing class will not compile due to CS0245:
"The constraints for type parameter `T' of method
`DerivedClass.GenericMethod<T>()' must match the constraints for type parameter
`T' of interface method `InterfaceWithGenericMethod.GenericMethod<T>()'.
Consider using an explicit interface implementation instead"

This worked in 1.9.2, but does not work on 2.2 or 2.4

Reproducible: Always

Steps to Reproduce:
1. Create program with the following code:
interface InterfaceWithGenericMethod {
    T? GenericMethod<T>() where T : struct;
}

public class DerivedClass : InterfaceWithGenericMethod {
    public T? GenericMethod<T>() where T : struct {
        return null;
    }
}

class Program {
    public static void Main(string[] args) { }
}

2. compile program
Actual Results:  
generic_method_from_interface.cs(6,15): error CS0425: The constraints for type
parameter `T' of method `DerivedClass.GenericMethod<T>()' must match the
constraints for type parameter `T' of interface method
`InterfaceWithGenericMethod.GenericMethod<T>()'. Consider using an explicit
interface implementation instead
generic_method_from_interface.cs(2,8): (Location of the symbol related to
previous error)

Expected Results:  
Should compile using mono compiler. Can be compiled with .NET C# compiler and
will execute just fine on mono.

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