Why is string.Split(';') valid but string.Split(':',StringSplitOptions.RemoveEmptyEntries) is not?

Question

I'm confused which overload string.Split(';') is resolving to; I don't think ';' is a char array is it?

However, this is compiling OK but if I try to add a 2nd StringSplitOptions parameter no appropriate overload is found.

I don't like having to do new char []{';'} is it avoidable?

Answer 1

The first overload of String.Split() has parameters defined as

params char[] separator

This means you can pass any number of char parameters and it will work:

someString.Split('1', '2', '3');
// or just one separator
someString.Split(';');

The second overload is different, it defines parameters like this

char[] separator, StringSplitOptions options

Notice, there is no params. Which require you to pass char[] parameter:

someString.Split(new[] {'1', '2', '3'}, StringSplitOptions.None);
// or just one separator
someString.Split(new[] {';'}, StringSplitOptions.None);

Answer 2

In the first case you are using this method:

public string[] Split(params char[] separator)

In the second case:

public string[] Split(char[] separator, StringSplitOptions options)

As you can see the declaration in the second case is a little different, so you can't pass parameters in this way.

If you want to use this method in a similar way, you can write your own extension method:

public static class StringExtensions
{
    public static string[] Split(this string s, char separator, StringSplitOptions options)
    {
        return s.Split(new[] { separator }, options);
    }

//or

    public static string[] Split(this string s, StringSplitOptions options, params char[] separator)
    {
        return s.Split(separator, options);
    }
}

And use them like below:

        var s = "asdasd;asd;;";
        var split = s.Split(StringSplitOptions.RemoveEmptyEntries, ';');
        var split2 = s.Split(StringSplitOptions.RemoveEmptyEntries, ';', ',');
        var split3 = s.Split(';', StringSplitOptions.RemoveEmptyEntries);

I suggest you to read more about this elements:

1. string.Split()
2. params keyword
3. params keyword explanations: link

@Groo params keyword explanation:

The docs for params don't actually explain how/when the array gets created, so that's what's probably confusing. The thing is that params is just a hint to the compiler that you are allowed to pass your array's items separated by comma, without explicitly instantiating the array. But a new array containing your parameters is created on each call to the Split method, regardless of whether you are passing 0, 1 or many parameters. Also, you can still create an array yourself and pass it to the method, but this lets the compiler do it for you.