Usage of [in, out] in methods

Question

I want to ask if there is some difference between

public int Method1([In, Out] byte[] buffer);

and

public int Method2(byte[] buffer);

I came across http://referencesource.microsoft.com/#mscorlib/system/io/stream.cs,739 and wonder why [In, Out] is there?

Answer 1

Yes. There are differences.

• public int Method2(byte[] buffer); uses implicit In:

  Indicates that data should be marshaled from the caller to the callee, but not back to the caller.

• public int Method2(out byte[] buffer); uses Out:

  Indicates that data should be marshaled from callee back to caller.

• public int Method2(ref byte[] buffer); uses [In, Out].