Re: some trivial questions?

[Shark8 <onewingedshark@gmail.com>]

On Wednesday, November 1, 2017 at 12:44:20 PM UTC-6, tclwa...@gmail.com wrote:
> Why in ada, there is a separation between functions and procedures?
> Is there any real value in this?

Yes, there's a *LOT* of value here; the easiest way to illustrate this in conjunction with Private Types. Consider the following:

  Package Example is
    
    -- Handle is a monotonically increasing value, for the run of the program.
    Type Handle is private;
    
    Function Create Return Handle;
    Function Value( Object : Handle ) Return Positive;
    
  Private
    Type Handle is new Positive;
  End Example;

Everything that you really need to know about using the types and functions are given in the specification above. Below we have the actual implementation.


  Package Body Example is
    Count : Natural := 0;
    
    Function Create Return Handle is
    Begin
      Count:= Natural'Succ( Count );
      Return Handle( Count );
    End Create;
    
    Function Value( Object : Handle ) Return Positive is
      ( Positive(Object) );
    
  End Example;

> 
> Also why does is Use imply With? 

Because they are really about two different things:
WITH is really about dependency.
USE is about [direct] visibility.

> For example why do i have to say:
> 
> with Ada.Text_IO;
> use Ada.Text_IO;

Because "with Ada.Text_IO" is simply saying that you're depending on the "Text_IO" compilation-unit inside-or-subordinate-to the compilation-unit "Ada".

The "use Ada.Text_IO" is about importing the whole namespace "Ada.Text_IO" into the current visibility scope.

> Is there any case where the Use statement will be ambiguous, if i skip the with part?

You cannot skip the with part.