CODEWITHSUNDEEP
c#lambdaexpression
Mladen B.
Mladen B.

Reputation: 2996

Is it possible to call a method with the parameter of 'lambda expression'?

Let's say I have a method with the following signature:

public string Foo(Expression expression)
{
    ...
}

Is it possible to call this method directly, without using proxy methods, and if it is, how?

As a bonus question (to understand why am I trying to do this), is it possible to declare a single method (without overloads) which will be called in all these cases:

Foo(P p => "");
Foo((P p, Q q) => "");
Foo((P p, Q q, R r) => "");

The reason I'm trying to write this in a single method is because I'm only interested in the lambda expression parameter to parse it in some way, not to execute it.

Upvotes: 1

Views: 165

Answers (3)

Evk
Evk

Reputation: 101473

To call this method directly you need to cast expression you pass to specific expression delegate type. For example:

Foo((Expression<Func<P, string>>) ((P p) => ""));
Foo((Expression<Func<P, Q, string>>) ((P p, Q q) => ""));
Foo((Expression<Func<P, Q, R, string>>) ((P p, Q q, R r) => ""));
Expression<Func<P, string>> x = (P p) => "";
Foo(x); // also fine

The reason is otherwise compiler cannot infer type of delegate to use. Expression (P p) => "" has no type by itself, type is determined by the context. If you use it in context where delegate is expected, and it's compatible - it will be a delegate:

Func<P, string> x = (P p) => "";
MyDelegate x = (P p) => "";

If you use it in context where expression tree of specific delegate type is expected - it will be expression tree:

Expression<Func<P, string>> x = (P p) => "";

But in your case - its type cannot be inferred. It can be Expression<Func<P, string>>, Expression<MyCustomDelegate> or anything else. Different delegate types are not the same, even if they have the same signature. So you have to tell it explicitly.

Upvotes: 4

Tom
Tom

Reputation: 85

Declare a delegate with the params keyword.

Example:

public delegate void ParamsAction(params object[] args);

Then:

public void Foo(object[] args)
{
  ...
}

To use:

ParamsAction action = Foo;
action(p);
action(p, q);
action(p, q, r);

or:

ParamsAction action1 = p => "";
ParamsAction action2 = p, q => "";
ParamsAction action3 = p, q, r => "";

Upvotes: 0

Damitha Shyamantha
Damitha Shyamantha

Reputation: 534

yes, You can use as follows,

Foo(Expression<Func<TEntity, bool>> query)
{
      // implementation
}

call it as

Foo((x=> x.bar == 1));

you don't need to use overloads in above-mentioned method calls. use this method instead and pass whatever the lambda you want.

hope it helps :)

Upvotes: 0

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