前向声明与依赖解耦 | C++
本章覆盖：forward declaration；incomplete type；pointer / reference to incomplete type；complete type requirement；reduce include dependency；compile time；cyclic dependency；pImpl 的后续连接；不为减少 include 牺牲接口可读性。
本章知识点
- forward declaration
- incomplete type
- pointer / reference to incomplete type
- complete type requirement
- reduce include dependency
- compile time
- cyclic dependency
- pImpl 的后续连接
- 不为减少 include 牺牲接口可读性