Case insensitive compare string to non-string

Question

I created a C# struct which can generically handle case insensitive string comparisons, transparently. So for example:

List<IString> list = new List<IString>();
list.Add("help");
Assert.IsTrue(list.Contains("Help"));

or

Dictionary<IString, string> dict = new Dictionary<IString, string>();
dict["Help"] = "thanks!";
Assert.AreEqual("thanks!", dict["hELP"]);

But the one thing I can't figure out (and maybe it's not possible), is how to get class string to play nicely in .Equals(object):

IString A1 = "A";
string A2 = "a";
Assert.AreEqual(A1, A2, "This passes");
Assert.AreEqual(A2, A1, "This fails");

Here's the code:

using System;
using System.Collections.Generic;
namespace Util
{
 /// <summary>
 /// Case insensitive wrapper for the string class
 /// </summary>
 public struct IString :
 IComparer<IString>,
 IComparable,
 IComparable<IString>,
 IComparable<string>,
 IEquatable<string>,
 IEquatable<IString>
 {
 private const StringComparison icase = StringComparison.OrdinalIgnoreCase;
 public readonly string Value;
 public IString(string Value)
 {
 this.Value = Value;
 }
 public bool Equals(string Other)
 {
 return string.Equals(Value, Other, icase);
 }
 public bool Equals(IString Other)
 {
 return string.Equals(Value, Other.Value, icase);
 }
 public override bool Equals(object obj)
 {
 if (obj is IString || obj is string)
 {
 return string.Equals(Value, obj.ToString(), icase);
 }
 else
 {
 return false;
 }
 }
 public int IndexOf(string Other)
 {
 return Other.IndexOf(Other, icase);
 }
 public bool Contains(string Other)
 {
 return IndexOf(Other) >= 0;
 }
 public override int GetHashCode()
 {
 if (Value == null)
 return 0;
 else
 return StringComparer.OrdinalIgnoreCase.GetHashCode(Value);
 }
 public override string ToString()
 {
 return Value;
 }
 public int Compare(IString x, IString y)
 {
 return string.Compare(x.Value, y.Value, icase);
 }
 public int Compare(string x, string y)
 {
 return string.Compare(x, y, icase);
 }
 public int CompareTo(object obj)
 {
 if (obj is IString)
 return Compare(this, (IString)obj);
 else if (obj is string)
 return Compare(Value, (string)obj);
 else if (Value != null)
 return Value.CompareTo(obj);
 else
 return -1;
 }
 public int CompareTo(IString other)
 {
 return Compare(this, other);
 }
 public int CompareTo(string other)
 {
 return Compare(Value, other);
 }
 public static implicit operator string(IString From)
 {
 return From.Value;
 }
 public static implicit operator IString(string From)
 {
 return new IString(From);
 }
 #region IString to IString operators
 public static bool operator ==(IString Str1, IString Str2)
 {
 return string.Equals(Str1.Value, Str2.Value, icase);
 }
 public static bool operator !=(IString Str1, IString Str2)
 {
 return !string.Equals(Str1.Value, Str2.Value, icase);
 }
 public static IString operator +(IString Str1, IString Str2)
 {
 return (IString)(Str1.Value + Str2.Value);
 }
 public static bool operator >(IString Str1, IString Str2)
 {
 return Str1.CompareTo(Str2) > 0;
 }
 public static bool operator >=(IString Str1, IString Str2)
 {
 return Str1.CompareTo(Str2) >= 0;
 }
 public static bool operator <(IString Str1, IString Str2)
 {
 return Str1.CompareTo(Str2) < 0;
 }
 public static bool operator <=(IString Str1, IString Str2)
 {
 return Str1.CompareTo(Str2) <= 0;
 }
 #endregion IString to IString operators
 #region string to IString operators
 public static bool operator ==(string Str1, IString Str2)
 {
 return string.Equals(Str1, Str2.Value, icase);
 }
 public static bool operator !=(string Str1, IString Str2)
 {
 return !string.Equals(Str1, Str2.Value, icase);
 }
 public static IString operator +(string Str1, IString Str2)
 {
 return (IString)(Str1 + Str2.Value);
 }
 public static bool operator >(string Str1, IString Str2)
 {
 return Str2.CompareTo(Str1) < 0;
 }
 public static bool operator >=(string Str1, IString Str2)
 {
 return Str2.CompareTo(Str1) <= 0;
 }
 public static bool operator <(string Str1, IString Str2)
 {
 return Str2.CompareTo(Str1) > 0;
 }
 public static bool operator <=(string Str1, IString Str2)
 {
 return Str2.CompareTo(Str1) >= 0;
 }
 #endregion string to IString operators
 #region IString to string operators
 public static bool operator ==(IString Str1, string Str2)
 {
 return string.Equals(Str1.Value, Str2, icase);
 }
 public static bool operator !=(IString Str1, string Str2)
 {
 return !string.Equals(Str1.Value, Str2, icase);
 }
 public static IString operator +(IString Str1, string Str2)
 {
 return (IString)(Str1.Value + Str2);
 }
 public static bool operator >(IString Str1, string Str2)
 {
 return Str1.CompareTo(Str2) > 0;
 }
 public static bool operator >=(IString Str1, string Str2)
 {
 return Str1.CompareTo(Str2) >= 0;
 }
 public static bool operator <(IString Str1, string Str2)
 {
 return Str1.CompareTo(Str2) < 0;
 }
 public static bool operator <=(IString Str1, string Str2)
 {
 return Str1.CompareTo(Str2) <= 0;
 }
 #endregion IString to string operators
 }
}

Is there any way to get string.Equal(object) to actually deal with IString as a string?

• SLaks: You should use OrdinalIgnoreCase instead of InvariantCultureIgnoreCase; it's faster and more secure.
• SLaks: Also, return StringComparer.OrdinalIgnoreCase.GetHashCode(Value);.
• SLaks: Other than that, and the fact that it's not necessary in the first place, your struct looks pretty good.
• Bryce Wagner: @SLaks: OK, I'll switch to Ordinal. @CodeInChaos: Yeah, I agree that IString looks like an interface. But part of the reason for wanting this is for brevity, to avoid a bunch of "StringComparison.OrdinalIgnoreCase" stuff all over, to make code more readable. So if someone has a suggestion for a better name, I'm certainly interested.
• SLaks: @Bryce: How about InsensitiveString or CaselessString or UncasedString?

Answer 1

You don't need to create such a type in the first place.
Instead, you should use the StringComparer class.

For example:

var dict = new Dictionary<String, string>(StringComparer.OrdinalIgnoreCase);
dict["Help"] = "thanks!";
Assert.AreEqual("thanks!", dict["hELP"]);

Or

List<String> list = new List<String>();
list.Add("help");
Assert.IsTrue(list.Contains("Help", StringComparer.OrdinalIgnoreCase));

Also note that it shouldn't be named IString; only interfaces should begin with I.

To answer your question, no; that's impossible.

Answer 2

No there is not. The String.Equals(object) method has a hard dependency on the provided value being of the type String. It does a CLR type check which does not consider any user defined conversions or functions and hence will only work with an instance of System.String