Move semantics and function order evaluation

Question

Suppose I have the following:

#include 
struct A { int x; };

class B {
  B(int x, std::unique_ptr a);
};

class C : public B {
  C(st         


        

Answer 1

Use list initialization to construct B. The elements are then guaranteed to be evaluated from left to right.

C(std::unique_ptr a) : B{a->x, std::move(a)} {}
//                         ^                  ^ - braces

From §8.5.4/4 [dcl.init.list]

Within the initializer-list of a braced-init-list, the initializer-clauses, including any that result from pack expansions (14.5.3), are evaluated in the order in which they appear. That is, every value computation and side effect associated with a given initializer-clause is sequenced before every value computation and side effect associated with any initializer-clause that follows it in the comma-separated list of the initializer-list.