How can System.String be properly wrapped for case-insensitivy?

Question

This question is not about managing Windows pathnames; I used that only as a specific example of a case-insensitive string. (And I if I change the example now, a w

Answer 1

I would create an immutable struct that hold a string, converting the string in the constructor to a standard case (e.g. lowercase). Then you could also add the implicit operator to simplify the creation and override the compare operators. I think this is the simplest way to achieve the behaviour, plus you get only a small overhead (the conversion is only in the constructor).

Here's the code:

public struct CaseInsensitiveString
{
    private readonly string _s;

    public CaseInsensitiveString(string s)
    {
        _s = s.ToLowerInvariant();
    }

    public static implicit operator CaseInsensitiveString(string d)
    {
        return new CaseInsensitiveString(d);
    }

    public override bool Equals(object obj)
    {
        return obj is CaseInsensitiveString && this == (CaseInsensitiveString)obj;
    }

    public override int GetHashCode()
    {
        return _s.GetHashCode();
    }

    public static bool operator ==(CaseInsensitiveString x, CaseInsensitiveString y)
    {
        return x._s == y._s;
    }

    public static bool operator !=(CaseInsensitiveString x, CaseInsensitiveString y)
    {
        return !(x == y);
    }
}

Here is the usage:

CaseInsensitiveString a = "STRING";
CaseInsensitiveString b = "string";

// a == b --> true

This works for collections as well.