PhuwadonV / Cpp-Interface-Example

C++ Interface

Cpp-Interface-Example

Reduce interface-implemented class size

• Native syntax : class size grow along with the amount of implemented interface
• This repo syntax : +4 bytes for x86 | +8 bytes for x64

class IA {
public:
  virtual void f() = 0;
};

template<typename T>
class IB {
public:
  virtual T g() = 0;
};

// x86 : sizeof(A_Native) = 12
// x64 : sizeof(A_Native) = 20 => 24(Alignment)
class A_Native : public IA, public IB<void> {
protected:
  int i;
public:
  inline A_Native(int i) : i(i) {};

  virtual void f();
  virtual void g();
};

// x86 : sizeof(B_Native<int>) = 16
// x64 : sizeof(B_Native<int>) = 24 => 32(Alignment)
template<typename T>
class B_Native : public A_Native {
protected:
  int j;
public:
  inline B_Native(int i, T j) : A_Native(i), j(j) {};

  void f() override;
  void g() override;
};

// x86 : sizeof(A) = 8                   // sizeof(A_Native) - sizeof(A) = 4
// x64 : sizeof(A) = 12 => 16(Alignment) // sizeof(A_Native) - sizeof(A) = 8
class A {
  INTERFACES_BEGIN
    INTERFACE(IA)
    INTERFACE(IB<void>)
  NTERFACES_END
  int i;
public:
  inline A(int i) : i(i) {};
};

// x86 : sizeof(B<int>) = 12                  // sizeof(B_Native<int>) - sizeof(B<int>) = 4
// x64 : sizeof(B<int>) = 16 => 24(Alignment) // sizeof(B_Native<int>) - sizeof(B<int>) = 8
template<typename T>
class B : public A {
  INTERFACES_BEGIN
    INTERFACE(IA)
    INTERFACE(IB<void>)
  INTERFACES_END
  T j;
public:
  inline B(int i, T j) : A(i), j(j) {};
};