Re: Unbounded Strings

[Mark Lorenzen <mark.lorenzen@ofir.dk>]

Jeffrey Carter <spam@spam.com> writes:

> Andrew Carroll wrote:
>

[snip]

>
>> I found myself desingning more and debugging less.  There were still
>> problems
>> of course, such as pass by value or pass by reference; I didn't know what to
>> use
>> nor did I know if I had to specify it.  I found out when I created my first
>> graph,
>> you have to specify out paramter or in and out for the parameter or you get
>> a
>> copy instead of the actual "thing".
>
> This represents a serious misunderstanding of Ada parameter modes. All
> elementary types are passed by copy, regardless of the parameter
> mode. All tagged and limited types are passed by reference, regardless
> of the parameter mode. For all other types, the compiler chooses the
> parameter mode best suited to the type. Mode in means the subprogram
> receives a value from the caller, and cannot modify it; out means the
> subprogram provides a value to the caller, and in out means the caller
> provides a value which the subprogram may modify. Parameter modes have
> nothing to do with parameter passing mechanisms. See ARM 6.2.
>

Hint to Andrew: Don't think about _how_ parameters are passed (i.e. by
copy or by reference) for "For all other types" as Jeffrey says
above. Use "in", "in out" and "out" to express your _intentions_ with
the parameters. Don't worry about efficientcy - the compiler will do
"the right thing".

- Mark