In C++, what categories (lvalue, rvalue, xvalue, etc.) can expressions that produce temporaries of class type fall into?

Question

Here is some example code:

#include 

class Foo
{
public:
  explicit Foo(int x) : data(x) {};

  Foo& operator++()
  {
    data += 1;
            


        

Answer 1

Any expression in C++ is either an lvalue or an rvalue. Hence, you're asking for the classifications that are rvalues. For that, inspect the figure showing the tree of classifications, in the C++11 standard §3.10/1.

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For more info (without delving into the standard) see What are rvalues, lvalues, ....

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Regarding

“Are expressions like Foo(5) rvalues or prvalue”

a prvalue is necessary an rvalue – for it couldn't very well be an lvalue.

A prvalue “(“pure” rvalue) is an rvalue that is not an xvalue”, and an xvalue is “the result of certain kinds of expressions involving rvalue references” A constructor call does not produce an rvalue reference, hence it's not an xvalue. So the rvalue is a prvalue, a pure rvalue.