Replacing a string with multiple invocations of the replace() function

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Hello, my question is a bit weird. Suppose I have this piece of code:

C#

public class Program
{
	public static void Main()
    {
		const string SiteAssets = "siteassets";
		const string SysSiteAssets = "syssiteassets";

	    string text = $"{SiteAssets}/12345";

		text = text.Replace(SiteAssets, SysSiteAssets);
		text = text.Replace(SiteAssets, SysSiteAssets);

		Console.WriteLine(text);

		Console.ReadLine();
	}


}

I'm getting "syssyssiteassets/12345" in the console. How do I change the code to receive just "syssiteassets/12345", no matter how many times this line will be called?

C#

text = text.Replace(SiteAssets, SysSiteAssets);

What I have tried:

Seems easy enough, but I can't use REGEX, nor additional if statements to achieve this goal.

Posted 11-Jul-22 4:28am

Member 15341738

Updated 11-Jul-22 5:11am

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2 solutions

Solution 1

With a Replace, you can't - it's a very basic string match-and-replace function that doesn't do anything "clever". All it does is look for an exact match in the input string with the search string and does a direct replacement of it with the new string.
Since your replacement string contains the search string, it will always be found, and the Replace function has no concept of "start of string".

If you can't use a regex, then the only way to do it is to manually check is the input string starts with the search string, and only replace it if it does. But then you might as well use string.IndexOf and string.Substring yourself instead of Replace!

Posted 11-Jul-22 4:45am

OriginalGriff

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Graeme_Grant · Accepted Answer · 2022-07-11T05:11:00

You need to write an extension method for the string class ... something like:

C#

public static class StringExtensions
{
    public static string ReplaceIf(this string text, string oldValue, string newValue)
    {
        if (oldValue is null) throw new ArgumentException($"{nameof(oldValue)} is null");
        if (oldValue == string.Empty) throw new ArgumentException($"{nameof(oldValue)} is empty");
        // other qualifying test go here...

        if (text.Contains(newValue)) return text;

        return text.Replace(oldValue, newValue);
    }
}

Now you can do this:

C#

public class Program
{
    public static void Main()
    {
        const string SiteAssets = "siteassets";
        const string SysSiteAssets = "syssiteassets";

        string text = $"{SiteAssets}/12345";

        text = text.ReplaceIf(SiteAssets, SysSiteAssets);
        text = text.ReplaceIf(SiteAssets, SysSiteAssets);
        text = text.ReplaceIf(SiteAssets, SysSiteAssets);
        text = text.ReplaceIf(SiteAssets, SysSiteAssets);
        text = text.ReplaceIf(SiteAssets, SysSiteAssets);

        Console.WriteLine(text);

        Console.ReadLine();
    }
}

The output will be:

syssiteassets/12345

Enjoy!