Difference between the classes System.StringComparer and System.StringComparison?

Question

What is the difference between these two classes ?

I have used System.StringComparer.OrdinalIgnoreCase() and System.StringComparison.OrdinalIgnore

Answer 1

StringComparer is a Class which implements comparison interfaces like IComparer, IEqualityComparer, IComparer<String>, so that it can be used to compare two strings.

StringComparison is simply an Enum that you can pass in to certain methods to indicate which kind of comparison you want. In that case I suspect the underlying method would use a StringComparer to do the actual comparison.

When to use each

String specific methods like String.Equals only accepts a StringComparison value, so that's what you would use in this case.

You would use a StringComparer for methods which take a comparer as a parameter, and are called in a context where strings will be compared. For example, if you had a List<String>, and wanted to Sort that list in a case-insensitive way, you could do:

myList.Sort(StringComparer.OrdinalIgnoreCase);

Answer 2

The question is: why to have in a framework both of them ?

The explanation is this one:

• StringComparison is:

Specifies the culture, case, and sort rules to be used by certain overloads of the String.Compare and String.Equals methods

• StringComparer is:

Represents a string comparison operation that uses specific case and culture-based or ordinal comparison rules

Noticed a difference ?

In second case, so in case of StringComparer there is a notion of string comparison operation, but not string type.

In fact, if you look at this you will read simply:

Some non-string methods that have string comparison as a central operation use the StringComparer type.

An example, from the same link:

Array.BinarySearch(this.storedNames, name, StringComparer.Ordinal)

I use StringComparer like a comparison "base" among content of the array reference type.