CODEWITHSUNDEEP
c#delegatespredicate
John V
John V

Reputation: 5047

Can I use a standard delegate instead a predicate?

I know I can use an anonymous method or a lambda expression, e.g:

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


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

But I cannot figure out whether a regular delegate (delegate bool X (MyObject o) ) could be used, my attempts fail.

I.e. creating a delegate, set it to a method a then pass the delegate instance as the predicate.

Upvotes: 3

Views: 61

Answers (1)

Tewr
Tewr

Reputation: 3853

For compatibility reasons, you must instantiate the delegate explicitly, even if the signature of a different delegate is compatible. This is not very well documented, see discussion in this question.

Example for the (very verbose) syntax do do this:

public void Test()
{
    var l = new List<MyObject>();
    // The following three lines
    var x = new X(my => string.IsNullOrEmpty(my.Name));
    var p = new Predicate<MyObject>(x);
    l.RemoveAll(p);
    // ...will accomplish the same as:
    l.RemoveAll(my => string.IsNullOrEmpty(my.Name));
}

private delegate bool X(MyObject m);

private class MyObject
{
    public string Name { get; set; }
}

Upvotes: 2

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