Object-oriented Software in Ada 95

62 Procedures and functions
package Pack_Types is
type Miles is digits 8 range 0.0 .. 25_000.0;
type Kilometres is digits 8 range 0.0 .. 50_000.0;
end Pack_Types;
Then this package is made visible to the function M_To_K_Fun.
with Pack_Types; use Pack_Types;
function M_To_K_Fun(M:in Miles) return Kilometres is
Kilometres_Per_Mile : constant := 1.609_344;
begin
return Kilometres( M * Kilometres_Per_Mile );
end M_To_K_Fun;
Finally, in the main procedure in addition to the normal input and output packages the package Pack_Types
and the function M_To_K_Fun are made visible.
with Ada.Text_Io, Ada.Float_Text_Io, Pack_Types, M_To_K_Fun;
use Ada.Text_Io, Ada.Float_Text_Io, Pack_Types;
procedure Main is
No_Miles : Miles;
begin
Put("Miles Kilometres"); New_Line; No_Miles := 0.0;
while No_Miles 2, Exp=>0 ); Put(" ");
Put( Float( M_To_K_Fun( No_Miles ) ), Aft=>2, Exp=>0 );
New_Line; No_Miles := No_Miles + 1.0;
end loop;
end Main;
Note:
5.3 Procedures
It is only required to with the function M_To_K_Fun. It would be an error to use the function
M_To_K_Fun.
A procedure is a program unit that, unlike a function, does not return a result. If information has to be returned to
the calling environment this is done instead by writing to a formal parameter that has been declared as mode out.
Writing to the formal parameter of a procedure updates the value of the actual parameter passed to the procedure.
The full implications of modes of a parameter are discussed in Section 5.5.
type Miles is digits 8 range 0.0 .. 25_000.0;
type Kilometres is digits 8 range 0.0 .. 50_000.0;
procedure M_To_K_Proc(M:in Miles; Res:out Kilometres) is
Kilometres_Per_Mile : constant := 1.609_344;
begin
Res := Kilometres( M * Kilometres_Per_Mile );
end M_To_K_Proc;
Note:
A procedure can only export values back to the caller’s environment by writing to a parameter that has
mode out or in out.
© M A Smith - May not be reproduced without permission