Regular Expression replace specific characters

Question

Does anyone know of a better / cleaner way to write the following:

GetSafeTagName(txtUserInput.text);
public static string GetSafeTagName(string tag)
{
 tag = tag.ToUpper()
 .Replace("'","`")
 .Replace('"','`')
 .Replace("&", "and")
 .Replace(",",":")
 .Replace(@"\","/"); //Do not allow escaped characters from user
 tag = Regex.Replace(tag, @"\s+", " "); //multiple spaces with single spaces
 return tag;
}

Thanks!

• user786653: Here is a SO question where the answer recommends using a StringBuilder.
• user15144: I once read an article by Jesse Liberty that said the decent support structure actually slowed the code down........

Answer 1

You could use a regular expression and Dictionary<string, string> to do the search replace:

// This regex matches either one of the special characters, or a sequence of 
// more than one whitespace characters.
Regex regex = new Regex("['\"&,\\\\]|\\s{2,}");
var map = new Dictionary<string, string> {
 { "'", "`"},
 { "\"", "`"},
 { "&", "and" },
 { ",", ":" },
 { "\\", "/" }
};
// If the length of the match is greater that 1, then it's a sequence
// of spaces, and we can replace it by a single space. Otherwise, we
// use the dictionary to map the character.
string output = regex.Replace(input.ToUpper(), 
 m => m.Value.Length > 1 ? " " : map[m.Value]);

• detay: As elegant as it may seem, sadly this alternative is 3 times slower.

Answer 2

When I had to do something similar, I used a Dictionary<string, string> to define the replacements.

And then something like this to replace:

foreach( KeyValuePair<string, string> pair in replacements)
{
 str = str.Replace(pair.Key, pair.Value);
}

http://msdn.microsoft.com/en-us/library/5tbh8a42.aspx

Answer 3

I think your method is pretty readable and clean as it stands. However, if you want to simplify the method itself, I have a decent support structure that would do so and possibly speed it up for particularly long strings:

internal static partial class SafeTag
{
 private static readonly IEnumerable<Replacement> _Replacements =
 [
 new Replacement("'", "`"),
 new Replacement("\"", "`"),
 new Replacement("&", "and"),
 new Replacement(",", ":"),
 new Replacement("\\", "/"),
 ];
 private static readonly Regex _Spaces = Spaces();
 public static string GetSafeTagName(this string tag)
 {
 StringBuilder parse = new(tag.ToUpper());
 parse = _Replacements.Aggregate(
 parse,
 (current, replacement) => current.Replace(replacement.Original, replacement.ToReplaceWith));
 return _Spaces.Replace(parse.ToString(), " ");
 }
 private readonly struct Replacement(string original, string toReplaceWith)
 {
 public string Original { get; } = original;
 public string ToReplaceWith { get; } = toReplaceWith;
 }
 [GeneratedRegex("\\s+", RegexOptions.Compiled)]
 private static partial Regex Spaces();
}