Re: Untyped "constant"?

[jbg@sei.cmu.edu (John Goodenough)]

In article Untyped "constant"? of 23 Sep 91 16:44:46 GMT
gralia@ddsdx2.jhuapl.edu (Mars J. Gralia) writes: 

>a) Suppose I have a compiler/RTE in which integer'last is 32_767.
>b) And suppose the system has a long_integer type in which
>   long_integer'last = 2_147_483_647.
>c) And suppose I have the program:
>          procedure Named1 is
>             X : constant := integer'last+5;
>          begin
>              for j in 1..X loop
>                  null;
>              end loop;
>          end Named1;

>Then:  is this a legal program or not?

The named number declaration is illegal, because INTEGER'LAST is of type
INTEGER (see 3.5(9)) and the initialization expression for a named number must
have a universal type (see 3.2.2(1)).  So suppose you fix this problem by
writing:

	X : constant := INTEGER'POS(INTEGER'LAST) + 5;

Note that INTEGER'POS returns a value of type universal integer (see 3.5.5(6)),
INTEGER'LAST is a static expression (4.9(8)), and INTEGER'POS(INTEGER'LAST) is
static (4.9(8)).

But this doesn't solve the problem, since

	for J in 1..X loop

is now equivalent to

	for J in 1..32_767+5 loop

The upper and lower bounds of this range will be converted to the predefined
INTEGER type (3.6.1(2)), and this conversion will raise CONSTRAINT_ERROR.



John B. Goodenough					Goodenough@sei.cmu.edu
Software Engineering Institute				412-268-6391