Re: integer questia

[Robert A Duff <bobduff@shell01.TheWorld.com>]

bedriemir <bedriemir@gmail.com> writes:

> what is the relation of root_integer , universal_integer and Integer

universal_integer is sort of like root_integer'Class.

All integer types you declare are implicitly derived from
root_integer.  Integer, which is Standard.Integer, is 
derived from root_integer as usual.  "Integer" is badly named
(since it's not the true infinite set of integers),
and Standard is badly named (since it contains types
like Integer with non-standard, implementation-defined
ranges).  Typically, Integer has a range of -2**31..2**31-1.

Most of the time, root_integer and universal_integer expressions
have static values (known at compile time), and therefore have
infinite range.  For example, you can say:

    N : constant := 2**999;

even though your computer doesn't have 999 bits in a machine integer.
At run-time, however, root_integer and universal_integer expressions
will use the largest integer type supported at run time (64-bits,
in GNAT).

- Bob