About the matter that the code to read the C structure member (Char array) that was working in swift 2.3 in swift 3 did not work

When operating a C structure like the one below from swift via bridge

cstruct.h

 #define MEM01_SIZE 255
 struct cstruct {
    char cstr01[MEM01_SIZE];
  } 

In swift2, it was made with the following code, but in swift3, it was a compiler error.

swift:swift2.2.swift

var size: Int32 = 0
var cstruct = GetCStruct(&size)
let cstr01_str = withUnsafePointer(&cstruct.memory.cstr01)
{
 return String.fromCString(UnsafePointer($0))!
}

In swift3, I passed by doing the following.

swift3.swift

var cstr01_str_tuple = cstruct?.pointee.cstr01
let cstr01_str = withUnsafePointer(to: &cstr01_str_tuple)
{
  return String(cString: UnsafeRawPointer($0).assumingMemoryBound(to: CChar.self))
}

I'm not sure why it works, so I can't write a commentary yet, but it worked for the time being, so make a note.