CODEWITHSUNDEEP
c#.net
user610650
user610650

Reputation:

Can named arguments be used with the params modifier?

I am trying to invoke Invoke on a Dispatcher using the following overload:

public object Invoke(Delegate method, params object[] args);

I want to use named arguments, but I can't seem to find the syntax for the argument with the params modifier. All of the following won't compile:

dispatcher.Invoke(method: () => { }, args: {});
dispatcher.Invoke(method: () => { }, args: new object[0]);
dispatcher.Invoke(method: () => { }, args: null);
dispatcher.Invoke(method: () => { }, args: new object[] {});
object[] foo = {};
dispatcher.Invoke(method: () => { }, args: foo);
dispatcher.Invoke(method: () => { }, args: new[] {"Hello", "World!"});

I found these two questions to which there seems to be no definite answers:

Named parameters with params

How to set named argument for string.Format?

So my question is: can it be done or not? If yes, how?

UDPATE

Daniel Hilgarth's shows that yes params can be used with named parameters. I integrated his answer using this pattern:

Action method = () => { };
if (_dispatcher != null)
    _dispatcher.Invoke(method: method, args: null);
else
    method();

Upvotes: 6

Views: 1998

Answers (2)

Daniel Hilgarth
Daniel Hilgarth

Reputation: 174299

The following code compiles without problems:

void Main()
{
    Invoke(method: () => {}, args: new object[] {});
}

public object Invoke(Action method, params object[] args)
{
    return null;
}

I had to change the type of the first parameter from Delegate to Action to make it compile, because () => {} can't be converted to Delegate.

Alternatively, the following does also compile:

void Main()
{
    Action method = () => {};
    Invoke(method: method, args: new object[] {});
}

public object Invoke(Delegate method, params object[] args)
{
    return null;
}

My assumption is that you never got a compile error about the args parameter but about the method parameter saying "Cannot convert from 'lambda expression' to 'System.Delegate'". This problem is solved by either casting the lambda to an Action (Invoke(method: (Action)(() => {}) ...) or by defining a variable of type Action that is passed as parameter to the method (see above), because Action can implicitly be converted to Delegate.

Upvotes: 3

daryal
daryal

Reputation: 14919

Have a try;

dispatcher.Invoke(method: () => { }, args: new[] {"Hello", "World!"});

Upvotes: 2

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