[Mono-bugs] [Bug 429081] New: Method overload resolution incorrectly generates CS0121 for unambiguous case

[bugzilla_noreply at novell.com]

https://bugzilla.novell.com/show_bug.cgi?id=429081


           Summary: Method overload resolution incorrectly generates CS0121
                    for unambiguous case
           Product: Mono: Compilers
           Version: 1.9
          Platform: Other
        OS/Version: Other
            Status: NEW
          Severity: Normal
          Priority: P5 - None
         Component: C#
        AssignedTo: mono-bugs at lists.ximian.com
        ReportedBy: marc.gravell at gmail.com
         QAContact: mono-bugs at lists.ximian.com
          Found By: Community User


Description of Problem:
Ambiguous call reported [between int and long? overload], even though there is
a clear "best" (14.4.2.2) overload that doesn't involve an implicit conversion

Steps to reproduce the problem:
Code as below, compile with gmcs [compiles fine with csc].

Actual Results:
test.cs(25,25): error CS0121: The call is ambiguous between the following
method
s or properties: `Program.Average<Bar>(IDataProducer<Bar>, FooFunc<Bar,long?>)'
and `Program.Average<Bar>(IDataProducer<Bar>, FooFunc<Bar,int>)'
test.cs(29,33): (Location of the symbol related to previous error)
Compilation failed: 1 error(s), 0 warnings

Expected Results:
Should compile, selecting the "int" overload.

How often does this happen? 
Every time

Code:

using System;

// same as Func<,> - just named to avoid 3.5 confusion
delegate TResult FooFunc<TArg,TResult>(TArg arg);

interface IDataProducer<T> {
  // implementation not needed to show error
}

interface IFuture<T> {
  // implementation not needed to show error
}

// a POD-type with a value we will aggregate later
class Bar {
  public int Value {get;set;}
}

static class Program {
  static void Main()
  {
      // implementation not needed to show error
      IDataProducer<Bar> data = null;

      // throws CS0121 between "long?" and "int" overloads
      var result = data.Average(x=>x.Value);
  }

  // Average overload for int
  public static IFuture<double> Average<TSource>(
    this IDataProducer<TSource> source,
    FooFunc<TSource, int> selector)
  { // implementation not necessary to show bug
    throw new NotImplementedException();
  }

  // Average overload for long?
  public static IFuture<double?> Average<TSource>(
    this IDataProducer<TSource> source,
    FooFunc<TSource, long?> selector)
  { // implementation not necessary to show bug
    throw new NotImplementedException();
  }
}


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