How do you declare a Predicate Delegate inline?

Question

I'm using C#.

So I have an object which has some fields, doesn't really matter what. I have a generic list of these objects.

List<MyObject> myObjects = new List<MyObject>();
myObjects.Add(myObject1);
myObjects.Add(myObject2);
myObjects.Add(myObject3);

So I want to remove objects from my list based on some criteria. For instance, myObject.X >= 10. I would like to use the RemoveAll(Predicate<T> match) method for to do this.

I know I can define a delegate which can be passed into RemoveAll, but I would like to know how to define this inline with an anonymous delegate, instead of creating a bunch of delegate functions which are only used in once place.

Answer 1

There's two options, an explicit delegate or a delegate disguised as a lamba construct:

explicit delegate

myObjects.RemoveAll(delegate (MyObject m) { return m.X >= 10; });

lambda

myObjects.RemoveAll(m => m.X >= 10);

---

Addition:

Performance wise both are equal. As a matter of fact, both language constructs generate the same IL when compiled. This is because C# 3.0 is basically an extension on C# 2.0, so it compiles to C# 2.0 constructs :)

Answer 2

The lambda C# 3.0 way:

myObjects.RemoveAll(m => m.x >= 10);

The anonymous delegate C# 2.0 way:

myObjects.RemoveAll(delegate (MyObject m) {
   return m.x >= 10;
});

And, for the VB guys, the VB 9.0 lambda way:

myObjects.RemoveAll(Function(m) m.x >= 10)

Unfortunately, VB doesn't support an anonymous delegate.

Answer 3

  //C# 2.0
  RemoveAll(delegate(Foo o){ return o.X >= 10; });

or

  //C# 3.0
  RemoveAll(o => o.X >= 10);

or

  Predicate<Foo> matches = delegate(Foo o){ return o.X >= 10; });
  //or Predicate<Foo> matches = o => o.X >= 10;
  RemoveAll(matches);