Re: Properties

["Peter C. Chapin" <PChapin@vtc.vsc.edu>]

On 2010-12-04 00:35, Shark8 wrote:

> Just a quick question, but why was it necessary to have two sets of
> containers, one for the indefinates and one for the definites?

Each instance of an indefinite type can have different sizes. For example

procedure Example is
   S1 : String(1 .. 10);
   S2 : String(1 .. 100);
begin
  null;
end Example;

S1 and S2 occupy different amounts of memory. The indefinite containers
deal with this by using access values internally. That is an indefinite
vector of strings actually stores String access values (pointers) and
manages that extra indirection internally so you aren't exposed to it.
This allows strings of different sizes to be stored in the vector in a
uniform way. The price is extra overhead and slightly less efficiency.

Class wide types are also indefinite because an instance of a class wide
type can be one of several different types in the class (all with
potentially different sizes).

Peter