[munificent]

Presumably because it's not worth the memory hit to store the hash.

[DoggettCK]

That was my assumption, too. They do memoize the length, but I'm sure those bytes add up, having run into OutOfMemoryExceptions building huge amounts of strings before.

[reddiric]

Strings know their length in the CLR because they are represented as BSTRs

http://blogs.msdn.com/b/ericlippert/archive/2011/07/19/strin...

This lets them interoperate with OLE Automation.

[porges]

You have to store the length, C# strings can contain '\0' (although the hashing code doesn't take this into account!)