When to Use Member Initializer Lists

Member initializer lists provide several benefits over assigning values in the constructor body:

1. Performance: Initializing members in the initializer list directly constructs them with the provided values. Assigning values in the constructor body first default-constructs the members, then assigns to them. This can be less efficient, especially for complex types.
2. Const and Reference Members: Const and reference members MUST be initialized in the member initializer list, as they cannot be assigned to later.
3. Clarity: Initializer lists make it clear which arguments are being used to initialize which members. This can make the code more readable.

Here's an example:

1#include <string>
2
3class Player {
4public:
5  Player(const std::string& name, int health)
6      : name_{name}, health_{health} {}
7
8private:
9  std::string name_;
10  int health_;
11};

Without the initializer list, we would have to write:

1Player::Player(const std::string& name, int health) {
2  name_ = name;
3  health_ = health;
4}

This is less efficient, as name_ will be default-constructed first, then assigned to.

So prefer initializer lists, especially for const/reference members and complex types. Use assignment in the constructor body only when the initialization depends on some computation that can't be done in the initializer list.