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Newsgroups: comp.lang.ada
Date: Tue, 29 Jun 2021 12:25:25 -0700 (PDT)
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Subject: calling function but ignoring results
From: Matt Borchers <mattborchers@gmail.com>
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Xref: reader02.eternal-september.org comp.lang.ada:62298
List-Id: <comp.lang.ada>

It is not very often that ignoring a function result is okay, but I have ru=
n across many instances of the following block structure in code over the y=
ears:

declare
    dont_care : BOOLEAN;
begin
    dont_care :=3D foo( x, y );
end;

I also see the procedure wrapper used in some cases -- usually when exporte=
d in a package specification:

procedure FOO( x, y ) is
    b : BOOLEAN;
begin
    b :=3D foo( x, y );
end FOO;

The procedure adds nothing to the code except another thing to maintain whe=
n the function interface needs modification.

Is there a Ada 202x feature to support calling functions and ignoring the r=
esult?  If not, I'm wondering if the @ symbol recently introduced for assig=
nments could be used?  How would people feel about the following?

@ :=3D foo( x, y );

This would discard the result of the function.  This could obviously lead t=
o memory leaks (without reference counting), but the syntax could be restri=
cted for use on functions that do not return uncontrolled access types or t=
hese functions could be marked with a keyword to make it legal for it to be=
 called in such a way when the programmer knows that the access returned sh=
ould not be "freed" by the caller (such as a pointer into an existing struc=
ture).

I have not given this much thought so I'm sure there are reasons why this c=
an't (or shouldn't) be done in general.  Regardless, there are probably man=
y that would agree with me that the declare block and the wrapper procedure=
 options are annoying and could be considered superfluous for lack of a bet=
ter way to write the code more simply.

Matt