André,
On 4/4/21 06:23, André Warnier (tomcat/perl) wrote:
Hi.
I have a question which may be totally off-topic for this list, but this
has been puzzling me for a while and I figure that someone here may be
able to provide some clue as to the answer, or at least some interesting
ponts of view.
In various places (including on this list), I have seen multiple
occurrences of a certain way to write a test, namely :
if (null == request.getCharacterEncoding()) {
as opposed to
if (request.getCharacterEncoding() == null) {
Granted, the two are equivalent in the end.
But it would seem to me, maybe naively, that the second form better
corresponds to some "semantic logic", by which one wants to know if a
certain a-priori unknown piece of data (here the value obtained by
retrieving the character encoding of the current request) is defined
(not null) or not (null).
Said another way : we don't want to know if "null" is equal to anything;
we want to know if request.getCharacterEncoding() is null or not.
Or in yet another way : the focus (or the "subject" of the test) here is
on "request.getCharacterEncoding()" (which we don't know), and not on
"null" (which we know already).
Or, more literarily, given that the syntax of most (all?) programming
languages is based on English (if, then, else, new, for, while, until,
exit, continue, etc.), we (*) do normally ask "is your coffee cold ?"
and not "is cold your coffee ?".
On the other hand, in English, coffee which is not hot is called "cold
coffee" but in e.g. Spanish, it's "coffee cold".
So why do (some) people write it the other way ?
I personally put the null first because of my background in C. C
compilers (especially older ones) would happily compile this code
without batting an eyelash:
char *s;
s = call_some_function();
if(s = null) {
// do some stuff
}
Guess what? "Do some stuff" is always executed, and s is always null.
If you switch the operands, the compiler will fail because you can't
assign a value to null:
if(null = s ) {
// Compiler will refuse to compile
}
So it's a defensive programming technique for me.
Is it purely a question of individual programming style ?
Perhaps at this stage in history, it is only "style". But it does have a
practical
Is there some (temporary ?) fashion aspect involved ?
Do the people who write this either way really think in a different way ?
Or is there really something "technical" behind this, which makes one or
the other way be slightly more efficient (whether to compile, or
optimise, or run) ?
(*) excepting Yoda of course
-chris
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