Note the use of the constructor and destructor calls at the end - it might not be necessary to do it this way here (since they should be separate values, the assignment might be safe), but this is bulletproof.
例38-1 shows a small demonstration of calling a user function. The code calls a function that's supplied to it as argument and directly passes this function's return value through as its own return value. Note the use of the constructor and destructor calls at the end - it might not be necessary to do it this way here (since they should be separate values, the assignment might be safe), but this is bulletproof.