Split string with adding separator to substring

Question

I wrote my Split() extension, it's main goal is to save delimiters and add them to splitted strings.

For example:
I have a string "-1-2+3+4-5-6", and separators '+', '-' and I want to have following: "","-1","-2","+3","+4","-5","-6" or "-","1-","2+","3+","4-","5-","6" depends on input separator option.

My extension method consists of three parts:

1. Check input values;
2. Getting all indexes of separators, and separators in source string;
3. Split source string and adding separators to left or right substring.

Code:

public enum SeparatorOptions
{
    None = 0,
    AddSeparatorToLeftSubstring = 1,
    AddSeparatorToRightSubstring = 2
}
public static class Extensions
{
    public static string[] Split(this string source, char[] separators, SeparatorOptions separatorOptions)
    {
        if (separatorOptions < SeparatorOptions.None || separatorOptions > SeparatorOptions.AddSeparatorToRightSubstring)
        {
            throw new ArgumentException("Arg_SeparatorEnumIllegalVal");
        }
        if (separators == null || separators.Length == 0)
        {
            return source.Split((char[])null);
        }
        if (separatorOptions == SeparatorOptions.None)
        {
            return source.Split(separators);
        }
        // Getting all indexes of separators, and separators in source string
        int foundCount = 0;
        int[] separatorIndexes = new int[source.Length];
        char[] separatorValues = new char[source.Length];
        for (int i = 0; i < source.Length; i++)
            for (int j = 0; j < separators.Length; j++)
            {
                char separator = separators[j];
                if (source[i] == separator)
                {
                    separatorValues[foundCount] = source[i];
                    separatorIndexes[foundCount++] = i;
                    break;
                }
            }

        string[] splitString = source.Split(separators);
        // Adding separators to left or right substring
        if (separatorOptions == SeparatorOptions.AddSeparatorToLeftSubstring)
            return AddSeparatorToLeftSubstring(splitString, separatorValues, foundCount);
        if (separatorOptions == SeparatorOptions.AddSeparatorToRightSubstring)
            return AddSeparatorToRightSubstring(splitString, separatorValues, foundCount);
        return splitString;
    }
    private static string[] AddSeparatorToLeftSubstring(string[] splitString, char[] separatorValues, int foundCount)
    {
        for (int i = 0; i < foundCount; i++)
        {
            splitString[i] += separatorValues[i];
        }
        return splitString;
    }
    private static string[] AddSeparatorToRightSubstring(string[] splitString, char[] separatorValues, int foundCount)
    {
        for (int i = 1, j = 0; i <= foundCount; i++, j++)
        {
            splitString[i] = separatorValues[j] + splitString[i];
        }
        return splitString;
    }
}
class Program
{
    static void Main(string[] args)
    {
        string str = "-1-2+3+4-5-6";
        Console.WriteLine("Original split()");
        var res2 = str.Split(new char[] { '+', '-' }, SeparatorOptions.None);
        foreach (var el in res2) Console.WriteLine(el);
        Console.WriteLine("Add to right substring");
        var res = str.Split(new char[] { '+', '-' }, SeparatorOptions.AddSeparatorToRightSubstring);
        foreach (var elem in res) Console.WriteLine(elem);
        Console.WriteLine("Add to left substring");
        var res3 = str.Split(new char[] { '+', '-' }, SeparatorOptions.AddSeparatorToLeftSubstring);
        foreach (var el in res3) Console.WriteLine(el);
        Console.ReadKey();
    }
}

What I wrote seems to work, although I am not sure if it is the best way, or recommended way to do something like this, so I want to ask what is wrong with my code and how could it be done better.

Answer 1

Review

• You use very clean and strong names for all your variables so it's very easy to understand your code.
• You too often go without {}. Especially the double for loops become very confusing.
• You don't use good exception messages. In Arg_SeparatorEnumIllegalVal the Arg prefix is not necessary because the type of the exctpion is already telling me it's about an argument. You also formatted it like it was a variable with PascalCase but it's a message so it should be formatted like a normal sentence.

Alternative solution

There is a much shorter way to get the same results. You could use two different regexes:

var str = "-1-2+3+4-5-6";

Regex.Matches(str, "([-+]?[0-9]?)").Cast<Match>().Select(m => m.Value).Dump();
Regex.Matches(str, "([0-9]?[-+]?)").Cast<Match>().Select(m => m.Value).Dump();

which will respectively give you:

-1 
-2 
+3 
+4 
-5 
-6 
""

and

- 
1- 
2+ 
3+ 
4- 
5- 
6 
"" 

Whether you want to keep the empty string or not is up to you.

Answer 2

Can only pass a valid enum value so don't see the value in this:

if (separatorOptions < SeparatorOptions.None || separatorOptions > SeparatorOptions.AddSeparatorToRightSubstring)

Why oversize?

int[] separatorIndexes = new int[source.Length];
char[] separatorValues = new char[source.Length];

You could split first to get the proper length or use List

Don't skip { }

for (int i = 0; i < source.Length; i++)
{   
    char c = source[i]
    foreach(char separator in separators)
    {