Hello all,
I wrote a few months ago about a problem I was having with the new()
constraint on some generic abstract methods I was working with in a
project. Today, I was trying to update my project to mono 1.2, and I
noticed that the code no longer compiles. I distilled the issue down to a
sample code file I'm including.
It looks like the issue was fixed which prevented a generic method in a
derived class from overriding an abstract or virtual method in the base
class, in the cases where the base class defined a public parameterless
constraint (I don't know if this applies to other kinds of constraints.)
However, now, I am unable to call a second generic method that has the new()
constraint inside the derived method. It complains that the type T must
have a public parameterless constructor in order to use it in the function
invocation.
Does this make sense? Is there a workaround? I suppose I could fudge
things for now by implementing interfaces in the abstract and derived
classes, but I'd like this to just work. Any feedback appreciated.
following is the repro file.
cheers,
--ben
//BEGIN_FILE
using System;
namespace testConstraintsVirtuals
{
class MainClass
{
public static void Main(string[] args)
{
Console.WriteLine("Hello World!");
}
}
abstract class Base
{
public abstract void method<T>() where T : new();
}
class Derived : Base
{
// the first method signature is the ideal one. this one compiles
with ms csc. it's what you'd expect to do.
// in mono 1.1.17, you could remove the override, and specify
constraints, and it would compile, now no longer.
// gives error: The type `T' must have a public parameterless
constructor in order to use it as parameter `T' in the generic type or
method `testConstraintsVirtuals.Derived.method2<T>()'(CS0310)
public override void method<T>()
// public override void method<T>() where T : new()
// gives error: Cannot specify constraints for overrides or explicit
interface implementation methods
// public void method<T>() where T : new()
// gives error: testConstraintsVirtuals.Derived.method<T>()' hides
inherited abstract member
// new public void method<T>() where T : new()
// gives error: testConstraintsVirtuals.Derived.method<T>()' hides
inherited abstract member
{
method2<T>();
}
public void method2<T>() where T : new()
{
}
}
}
//END_FILE
--
ben joldersma
http://ben.creationsnetwork.org
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