C# expression Lambda

Question

Hi I'm learning about using Lambda from a book. After I copied a piece of code from the book to VS2010 I got the error:

Delegate 'System.Func<float>' does not take 1 arguments"

VS2010 marked the error under the left parenthesis at line 3, before "float x". Can you tell me what is wrong?

static void Main(string[] args)
{
    Func<float> TheFunction = (float x) =>
    {
        const float A = -0.0003f;
        const float B = -0.0024f;
        const float C = 0.02f;
        const float D = 0.09f;
        const float E = -0.5f;
        const float F = 0.3f;
        const float G = 3f;
        return (((((A * x + B) * x + C) * x + D) * x + E) * x + F) * x + G;
    };

    Console.Read();
}

Community · Accepted Answer · 2020-06-20 09:12:55Z

9

You're trying to write a function which accepts a float input, and returns a float output. That's a Func<float, float>. (To give a clearer example, if you wanted a delegate with an int parameter and a return type of float, that would be a Func<int, float>.)

A Func<float> would have no parameters, and a return type of float. From the documentation of Func<TResult>:

Encapsulates a method that has no parameters and returns a value of the type specified by the TResult parameter.
public delegate TResult Func<out TResult>()

edited Jun 20, 2020 at 9:12

CommunityBot

11 silver badge

answered Apr 23, 2015 at 21:27

Jon Skeet

1.5m893 gold badges9.3k silver badges9.3k bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Keith Nicholas Over a year ago

because you look a little short of rep +1

Yuval Itzchakov Over a year ago

@Garry You're voting for the answer, not the book.

p.s.w.g · Accepted Answer · 2015-04-23 21:27:26Z

4

Because a Func<T> represents a delegate which returns a value of type T. From MSDN:

Encapsulates a method that has no parameters and returns a value of the type specified by the TResult parameter.

What you want is a Func<float, float>—that is, a delegate which accepts a float as a parameter and returns a value of type float.

answered Apr 23, 2015 at 21:27

p.s.w.g

150k31 gold badges307 silver badges339 bronze badges

Comments

garryp · Accepted Answer · 2015-04-23 22:14:55Z

0

The final parameter in a Func is the return type, the others are the argument types. For Func with a, b, c as parameters, a and b are the argument types, c is the return type.

Func<int, int, double> func = (a,b) => a + b;
int aInt = 1;
int bInt = 2;
double answer = func(aInt, bInt); // answer = 3

answered Apr 23, 2015 at 22:14

garryp

5,7861 gold badge31 silver badges43 bronze badges

Collectives™ on Stack Overflow

C# expression Lambda

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related