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Impress your colleagues with your knowledge about…String.Intern

Sometimes when working with .NET you discover some hidden gems. Some of them very useful, other ones a little bit harder to find a good way to benefit from their functionality. One of those hidden gems that I discovered some days ago is String.Intern().

The String.Intern() method allows you to internalize string values explicitly. Ok, but what does this mean?

In a typical .NET application, the same string values are used over and over again. As this would end up with a lot of duplicated memory, .NET will allocate strings with unique content just once by using the string interning mechanism.

This leads to the question. As this interning is done for you, why do we need this method?  The thing is that only explicitly declared string literals are interned on the compile stage. The strings created at runtime are not checked for being already added to the string intern pool.

To solve this problem .NET offers two methods: String.Intern and String.IsInterned. If the string value passed to String.Intern is already in the pool, the method returns the reference to the string. Otherwise, the method adds the string to the pool and returns the reference to it. If you want to just check if a string is already interned, you should use the String.IsInterned method. It returns the reference to the string if its value is in the pool, or null of it isn’t.

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