C# pass function as argument

Question

Unfortunately, I cannot see this question in similar, so

I have to execute many similar functions, and I want to create one function that will accept functions as argument, e.g.

    int Search (Func<bool> func)
    {
        int start = Environment.TickCount;
        func();
        int end = Environment.TickCount;
        return end - start;
    }

    void SearchTime()
    { 
        int time1 = Search(list.Contains(item));
        int time2 = Search(dictionary.ContainsKey(anotheritem));
        /* some more code */
    }

But actually it says that the argument doesn't seem to be right.

UPD: The error says: The most appropriate overloaded method has some invalid arguments

@B.K. I don't actually have the same in arguments and I use existing funcs, but Guffa gave the exact answer. Maybe it's similar, but i don't find the answer in that subject — Olexiy Pyvovarov, Nov 08 '14 at 22:18

score 10 · Accepted Answer · answered Nov 08 '14 at 22:03

What you are trying to send into the method are not delegates.

You can use lambda expressions to create delegates for the method:

int time1 = Search(() => list.Contains(item));
int time2 = Search(() => dictionary.ContainsKey(anotheritem));

The () represents zero input parameters.

score 2 · Answer 2 · answered Nov 08 '14 at 22:31

What you have done:

Search(list.Contains(item));

this will first evaluate the inner expression list.Contains(item), which is a boolean value, not a function with a boolean return value. Next, this value and not the function will be passed to Search(), which is not possible and results in a compiler error.

You have two choices: use lambda expressions as noted by Guffa already:

class Program
{
    static void Main(string[] args)
    {
        SearchTime();
    }

    static int Search(Func<bool> func)
    {
        int start = Environment.TickCount;
        func();
        int end = Environment.TickCount;
        return end - start;
    }

    static void SearchTime()
    {
        IList<string> list = new []{"item"};
        IDictionary<string, string> dictionary = new Dictionary<string, string> { { "key", "value" } };

        int ticks1 = Search(() => list.Contains("item")); // Note: use () =>
        int ticks2 = Search(() => dictionary.ContainsKey("key")); // Note: use () =>
        /* some more code */
    }
}

If you don't like the () => syntax, you can place code into separate methods:

class Program2
{
    static void Main(string[] args)
    {
        SearchTime();
    }

    static int Search(Func<bool> func)
    {
        int start = Environment.TickCount;
        func();
        int end = Environment.TickCount;
        return end - start;
    }

    static void SearchTime()
    {
        int ticks1 = Search(ListContains); // Note: do not use () on ListContains
        int ticks2 = Search(DictionaryContainsKey); // Note: do not use () on DictionaryContainsKey
        /* some more code */
    }

    static IList<string> list = new[] { "" };
    static bool ListContains()
    {
        return list.Contains("item");
    }

    static IDictionary<string, string> dictionary = new Dictionary<string, string> {{"key","value"}};
    static bool DictionaryContainsKey()
    {
        return dictionary.ContainsKey("key");
    }
}

C# pass function as argument

2 Answers2