C++ High Performance

Preserving the valid state

Take a look at the following example. If the branches_ = ot.branches_ operation throws an exception due to being out of memory (branches_ might be a very big member variable), the tree0 method will be left in an invalid state containing a copy of leafs_ from tree1 and branches_ that it had before:

struct Leaf { /* ... */ };struct Branch { /* ... */ };class OakTree {public:  auto& operator=(const OakTree& other) {    leafs_ = other.leafs_;    // If copying the branches throws, only the leafs has been    // copied and the OakTree is left in an invalid state    branches_ = other.branches_;     *this;  }  std::vector<Leaf> leafs_;  std::vector<Branch> branches_;};
auto save_to_disk(const std::vector<OakTree>& trees) {  // Persist all ...