Re: Tests in a software release

[Stefan.Lucks@uni-weimar.de]

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On Wed, 25 Oct 2017, Victor Porton wrote:

> Do you agree that a release (that is software for which debugging was
> finished) should have integer overflow tests but not array out of bounds
> tests (because array out of bounds is always a programming error, but
> integer overflow may happen in an innocent program)?


Firstly, depending on your programming conventions (or style) either 
exception can be an error, or both, or none. As a rule of thumb, if the 
possibility for the exception is anticipated and the exception is handled,
it is not an error. If you don't anticipate the exception to be raised, 
raising it is an error.

Here a simple example for a program where an out-of-bounds access to an 
array is not an error, and skipping the check would break the program:

with Ada.Text_IO;

procedure Example is

    type Counter_Array is array (Character range <>) of Integer;
    Counter: Counter_Array('a' .. 'z') := (others => 0);

begin
    while not Ada.Text_IO.End_Of_File loop
       declare
          C: Character;
       begin
          Ada.Text_IO.Get(C);
          Counter(C) := Counter(C) + 1;
          Ada.Text_IO.Put_Line(C & Integer'Image(Counter(C)));
       exception
          when others => null;
       end;
    end loop;
    for C in Counter'Range loop
       Ada.Text_IO.Put(Integer'Image(Counter(C)));
    end loop;
end Example;


Secondly, even if raising the exception is an error, why do you want to 
skip the check?

Raising the exception gives you at least the chance to shut down your 
program cleanly (try to close files you opened ...) and to write some 
debugging output.

Of course, if it turns out that your program is too slow, skipping either 
check may be an option. Ideally, you only do so after properly profiling 
your program and locally, for the parts of the program which are 
performance bottlenecks. Generally turning of some checks from scratch is 
premature optimization. (BTW, my general experience is that skipping 
overflow and out-of-bounds access checks improves the peformance only 
marginally.)



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