const initialization

Initialization of const objects can be delayed using ternary operator or IILE:

std::vector<byte> dumpedGamePak /* = ... */;
const std::size_t CGB_support_code = 0x0143;

enum class console : uint8 { dmg, cgb_compatible, cgb_only };

const console m_type = dumpedGamePak[CGB_support_code] == 0xC0 ? console::cgb_only : 
                       dumpedGamePak[CGB_support_code] == 0x80 ? console::cgb_compatible :
                                                                 console::dmg;

Ternary operator trick is available since C89. A more relaxed approach is using IILE:

Stmt Parser::forStatement() {
  consume(TokenKind::LeftParen, "Expect '(' after 'for'.");

  const Stmt initializer = [&]() -> Stmt {
    if (match(TokenKind::Semicolon))
      return boost::blank{};

    if (match(TokenKind::Var))
      return variableDeclaration();

    return expressionStatement();
  }();

  // ...
}