Re: When to hide implementation details

From:

ram@zedat.fu-berlin.de (Stefan Ram)

Newsgroups:

comp.lang.c++

Date:

24 Apr 2008 14:29:40 GMT

Message-ID:

<account-20080424162710@ram.dialup.fu-berlin.de>

Ralph <r30@et10.org> writes:

The only rule I could find is basically 'hide everything and when the
profiler says it is slow, unhide it'. Is this a good approach ?

  You hide the implementation, so that you can change it later
  without changing the interface, which might break clients.

  For example, this account class was found in the web:

class Account
{ public:
  Account( int myMoney ): moneyAmount( myMoney ){};
  int getMoney() const{ return moneyAmount; }
  private:
  int moneyAmount; };

  It exposes the type ?int? of its private field ?moneyAmount?
  in the interface. So, one can not change this field's type to
  ?long? later without breaking the interface (or not taking
  full advantage of this change).

  Exercise: Devise an account class that does not expose the
  type used internally to store the amount in its interface, so
  that this type can be changed later. (For example, it might
  be changed from ?double? to a type using a decimal value
  representation with arbitrary precision, while the interface
  is not being changed.)