Bug 21023 - C# compiler incorrectly handles the case where null is passed in place of a "params object[]" parameter
Summary: C# compiler incorrectly handles the case where null is passed in place of a "...
Alias: None
Product: Compilers
Classification: Mono
Component: C# ()
Version: 3.4.0
Hardware: PC Windows
: --- normal
Target Milestone: ---
Assignee: Bugzilla
Depends on:
Reported: 2014-07-01 14:57 UTC by Chris Howie
Modified: 2014-07-01 15:17 UTC (History)
1 user (show)

Is this bug a regression?: ---
Last known good build:

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Description Chris Howie 2014-07-01 14:57:57 UTC
On Mono 3.4.0, it appears that using null as an argument to Delegate.DynamicInvoke() when the corresponding parameter is a non-nullable value type results in the target delegate receiving the default value for that delegate.

Simple test case:

using System;

class TestCase
    static void Main()
        Delegate d = new Func<int, int>(i => i);


On Mono, this prints 0.  On MS.NET, it crashes with System.Reflection.TargetParameterCountException.
Comment 1 Chris Howie 2014-07-01 14:58:50 UTC
"default value for that delegate" should of course be "default value for that type".
Comment 2 Chris Howie 2014-07-01 15:10:38 UTC
Apparently this is an issue with the compiler, not the runtime.  If you use:

Console.WriteLine(d.DynamicInvoke(new object[] { null }));

Then the behavior is the same on both platforms (0 is printed).  So DynamicInvoke is working correctly; the issue is that the Mono C# compiler does not correctly handle the case where null is passed where "params object[]" is expected.

Microsoft's compiler handles the case by passing a null object[].

Mono's compiler handles the case by passing an object[] with a single null element.
Comment 3 Chris Howie 2014-07-01 15:17:02 UTC
Sorry, I don't think this is a compiler bug after all, but an issue with DynamicInvoke.  I am closing out this mess of a bug report and will re-open a proper one when I have all of the information sorted.