Re: for-loop parameters

[stt@houdini.camb.inmet.com (Tucker Taft)]

CMSC 330-4021 Student 23 (cs330a23@nova.umuc.edu) wrote:

: If a loop parameter in a for-loop statement should not be declared in the
: variable declaration list, how can the compiler determine what type the
: loop parameter belongs to? Thanks.  

The syntax for a "for" loop includes the ability to specify explicitly
the type of the loop parameter.  By default, it is determined by the
type of the low and high bound, and if both are "universal" integers, 
then it uses Standard.Integer as a fallback.

For example:

    for I in 1..10 loop  -- uses Standard.Integer

    for MI in My_Integer range 1..10 loop  -- uses My_Integer

    for J in An_Array'Range loop  -- uses index subtype of An_Array

    for K in 1..N loop  -- uses type of N (unless univesal, in which case
                        -- uses Standard.Integer)

    for C in Red .. Green loop  -- uses enum type of Red and Green
                                     (presuming there is only one
                                      such type with directly visible
                                      enumerals)

    for MC in My_Color range Red .. Green loop
                               -- in case there are 2 or more
                               -- enum types with directly visible
                               -- enumerals Red and Green

    for X in F(Y) .. G(Z) loop  -- uses result type of F and G

etc...

I would guess that in 98% of the cases, the explicit type can be
left out, especially if you typically avoid having "magic" numeric 
literals scattered about in your code.

See RM95 5.5(4) for the "for" loop syntax, and RM95 3.6(6,17-19)
for the explanation of discrete_subtype_definition.

--
-Tucker Taft   stt@inmet.com   http://www.inmet.com/~stt/
Intermetrics, Inc.  Burlington, MA  USA