Cannot convert method group to Action-CodePudding

I am stuck with this error but not sure how to fix it.

I am trying to pass a method as a parameter to another function as an action. I have an interface which defines two methods:

//ISegment interface
void SetNodeA(in INode node);
void SetNodeB(in INode node);

Next I create a segment and I want to pass this method into another function:

ISegment segment = GetSegment();
Execute(start, segment.SetNodeA);
Execute(end, segment.SetNodeB);

My execute function looks like this:

void Execute(in EndPoint point, in Action<INode> fnc)
{
    Verify(segment);
    Verify(point.Node);
    fnc?.Invoke(point.Node); //set the node
}

Problem is i get this error:

Argument 2: cannot convert from 'method group' to 'in Action'

Not sure what it means by method group here or how to fix it.

CodePudding user response：

The problem is that your SetNodeA and SetNodeB methods have an in parameter and you're trying to invoke them via an Action<T>, which does not support in, out, or ref parameters.

If you need to keep using in for those methods, then you can achieve that by creating a custom delegate type and use that instead of Action<T>:

public delegate void ActionWithInParam<T>(in T node);

Then, your Execute method would be something like this:

void Execute(in EndPoint point, ActionWithInParam<INode> fnc)
{
    Verify(segment);
    Verify(point.Node);
    fnc?.Invoke(point.Node); //set the node
}

CodePudding user response：

You need either remove in parameter modifier from SetNodeX signature or use custom delegate for second Execute parameter:

public interface ISegment
{
    void SetNodeA(in INode node);
    void SetNodeB(INode node); // in removed
}

public delegate void DelegateWithIn(in INode node);

void Execute(in EndPoint point, DelegateWithIn fnc)
{
}
void Execute1(in EndPoint point, Action<INode> fnc)
{
}

Execute(null, segment.SetNodeA); // uses custom delegate
Execute1(null, segment.SetNodeB); // uses Action

As I mentioned in the comments Action and Func delegates does not support in, out and ref parameter modifiers.