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c#visual-studio-2010lambda
Cal
Cal

Reputation: 867

C# expression Lambda

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();
}

Upvotes: 2

Views: 342

Answers (3)

garryp
garryp

Reputation: 5766

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

Upvotes: 0

Jon Skeet
Jon Skeet

Reputation: 1500055

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>()

Upvotes: 9

p.s.w.g
p.s.w.g

Reputation: 149000

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.

Upvotes: 4

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