Rationale Behind C++ Commandments (2) – Philosophy of C

Everything is seen as a bitstream

  • pointers are just integers to memory locations
    – [25] integer and pointers might be indistinguishable in signature resolution
  • code (CPU instructions) and addresses are treated the same way as a stream of data
    – concept of function pointers leads to lambda (functors)
    – classes came from structs containing data and function pointers (combined with namespaces)!
  • unchecked type declarations: the compiler trusts your interpretations of data
    – leads to run-time features such as overriding (virtual methods)
  • handles (pointers and references) has unrestricted power
    – [29] can const_cast it away if the handle is exposed (bad idea)

Performance-first design choice

  • do not pay performance penalty for features not used
    – static compilation and binding by default
    – unchecked type declarations (see above)
  • static compilation: the compiler tries to know everything at compile time
  • static binding by default (cheapest)
    – pay extra to use virtual methods (overriding)
    – [38] default parameter values are statically bound and not stored in vtable (i.e. overridden child method’s default values are ignored and parent’s default values are used ONLY WHEN called through up-casts)
  • inline is at the mercy of the optimizer (which can choose to emit an object if decided inlining is counter-productive). Mechanism that forces a function pointer to exist (pointing the function, virtual functions creates the pointer in vtable)

Toolchain

  1. preprocessor (parser & macros)
  2. compiler (create object files per translation unit, which is .c file in C)
    – access control (encapsulation) extends the old trick of emulating private in C++ through macros by marking functions as static (local within translation unit) in C.
  3. linker (combine object files and adjust the addresses)

Templates behaves like a combination of macros (copy-and-paste with parameters) except it’s spread across the toolchain like inline optimizations:

  • Code bloat (one copy per type combination)
  • Can only live in the header files (it’s a template, not realized code, so no object is emitted like a .cpp file)

Parsing (language design)

  • most vexing parse [Effective STL Item 6]: if something can be interpreted as a function declaration, it will be interpreted as a function declaration

Plain Old Data Types (C++ classes tried to emulate in their operator overloading behavior)

  • [15] allow (a=b)=c chaining by returning *this for operator=
  • [21] disallow rvalue assignment (a+b)=c by returning const object

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