Re: When did the bool type make it into the language?

<someone@somewhere.net> writes:


  What /is/ a type?

  A type is a flag/marker that tells how to interpret
  a certain recording (for example a bit sequence).

  For example, ?unsigned int i; signed int j;? create
  two objects of the same size, but with different types.

  These are compile-time types. When choosing how to
  translate an overloaded operator like ?+?, the
  compiler can use the type information to choose the
  appropriate compilation/implementation. The type
  information then is discarded and not available at
  run time.

  There also are run-time types, which actually is
  what OOP (polymorphism) is all about. One also can
  implement run-time types oneself in C or C++:

struct my_object
{ int tag; /* 0 = int, 1 = bool */
  union record
  { int int_value;
    int bool_value; /* 0 = false, otherwise true */ }}

  or, the OOP way:

struct MyObject
{ struct vtable * vtable_;
  ... }

  The above structs show how to actually implement
  a run-time boolean type in C.

  As others have said, one /cannot/ implement a
  /compile-time/ boolean type in C using #define
  or typedef. After

#define BOOL int

  or

typdef int BOOL

  , the declaration

BOOL b;

  does /not/ give the compiler any information other
  than b has the type /int/. However,

struct/union bool { int value; };

  should do the trick (to create a compile-time type
  ?bool?.)

  Also see:

http://www.gotw.ca/gotw/026.htm

  .