These are slides from a lecture on Red Flags in Programming that took place at an Israeli Open Source Developers meeting. Red flags in programming are signs that you likely made a mistake with your application design or code. Noticing and avoiding these mistakes help us write better code, at any language. The subject related to mostly dynamic (higher level) languages, even though the sample code is in Perl.

1. Red Flags in Programming
Doing things that are probably...
not good for us

2. Some words of caution...
­ We Perlers have a saying...
TIMTOWTDI
­ Be nice, no flaming
(only I'm allowed)
­ Not a Perl lecture, more like “bad
programming habits”
­ “Your mileage may vary”, “no batteries
included”, “don't drink and drive”

3. :
#1
ag
Repeated code
Fl
­ We overlook repeated patterns without even noticing
­ N more to read, understand, debug, test, maintain
­ N more places to have bugs!
­ Updating multiple places is error prone..
­ it's boring
­ distracting
­ lose focus
­ make mistakes
­ OMFG BUGZ!
­ Really, the worst thing a programmer can do

4. :
#1
ag
Repeated code
Fl
­ Abstract your code... correctly!
­ Class?
­ Abstract Class? (role)
­ Package?
­ Collection of Functions?
­ Loops?
­ Switches?
­ Dispatch tables?

5. :
#2
ag
Reinvent the Wheel
Fl
­ You probably won't do it better... seriously
­ Development and maintenance grows because you
now have another (usually big) chunk of code
­ It's just repeated code, really...

6. :
#2
ag
Reinvent the Wheel
Fl
­ Modules
­ Libraries
­ Roles
­ Frameworks
­ Whatever the hell [Free] Pascal has
­ Write patches for what doesn't work for you
­ In extreme cases reinvent, but try to implement
as little as required.
­ Sometimes it's necessary to do it all from scratch:
Perlbal, Git, Linux :)

7. :
#3
ag
Switches without default
Fl
­ Not always wrong if ( is_alpha($num) ) {}
­ Usually wrong
­ Unexpected behavior elsif ( is_numeric($num) ) {}
­ Not the worst of things...
but please think of it

8. :
#3
ag
Switches without default
Fl
if ( is_alpha($num) ) {}
elsif ( is_numeric($num) ) {}
else {
}

9. :
#4
ag
Long Switches
Fl
­ Gross, really given ($foo) {
­ Not fun to read or debug
­ Not easily maintainable when (/^10$/) {}
­ It's basically a long if() when (/^20$/) {}
elsif()... even if seems when (/^30$/) {}
otherwise default {}
}

10. :
#4
ag
Long Switches
Fl
­ Dispatch tables my %dispatch = (
(if you can)
­ Use code references in 10 => CODEREF,
switches instead of code 20 => CODEREF,
itself
30 => CODEREF,
(if you can)
);
$dispatch{$num}->();

11. :
#5
ag
Try and Catch (workflow)
Fl
­ Try and Catch isn't for try {
workflow!!
­ That's what we have do_something_simple();
conditions and loops for } catch {
­ Internal functions should
print “Dear god, this is a
have return codes, not
throw exceptions really stupid thing to do!”;
­ PHP is fscking stupid }
­ Try and Catch is for when
external functions might
crash the program

12. :
#5
ag
Try and Catch (workflow)
Fl
­ Functions, subroutines, do_something_simple()
return codes!
­ Try and Catch is for or die “you suck!n”;
external programs or
things that are suppose to
crash

13. :
#6
ag
String Booleans
Fl
­ The string “false” is if ( $bool eq 'true' ) {
actually true => confusing!
­ Unnecessary value DO SOMETHING
check/comparison } elsif ( $bool eq 'false' ) {
­ Misses the point of
DO SOMETHING
booleans.
}
$bool = 'false';
if ( $bool ) { BUG }

14. :
#6
ag
String Booleans
Fl
­ Use real booleans $bool = do_that(@params);
­ Use zero (0), empty
strings and undefined
variables if ($bool) {
­ Sometimes you can't
# wheee... actual booleans
control it (using modules,
etc.) }

15. :
#7
ag
External Binaries
Fl
­ Compatibility problems
­ Portability problems
­ Unexpected results (`ps` for example is different on BSD
and has different command line switches)
­ Insecure!

16. :
#7
ag
External Binaries
Fl
­ Shared libraries
­ Bindings
­ APIs
­ libcurl is an example
­ Modules for running binaries more safely and controllably
(IPC::Open3, IPC::Open3::Simple, IPC::Cmd,
Capture::Tiny)
­ Taint mode (if language supports it – Perl does!)
­ Sometimes you can't control it (external binaries, closed
programs, dependencies at $work)

17. :
#8
ag
Intermediate Programs
Fl
­ Quite possibly insecure
­ Hard to maintain
­ No damned syntax highlighting!!!11

18. :
#8
ag
Intermediate Programs
Fl
­ If same language, use a subroutine/function
­ Different language && use an Inline module
­ Else, use templates
­ External file

19. :
#9
ag
Empty if() Clauses
Fl
­ Not DWIM/SWYM if ( $something ) {
­ Having an empty if() for
the sake of the else().. is # do nothing
horrible } else {
CODE
}

20. :
#9
ag
Empty if() Clauses
Fl
­ SWYM... please? if ( !$something ) {
­ Use unless() [Perl]
­ Don't really use unless() CODE
}
unless ( $something ) {
CODE
}
* Shlomi Fish is allowed to do otherwise :)

21. 0:
#1
ag
Array Counters
Fl
­ Some older languages foreach my $i ( 0 .. $n ) {
have no way to know how
many elements are in an $array[$i] = 'something';
array... $array_counter++;
­ Some people are too
}
used to older (more low­
level) languages
­ Some people don't know
there's a better way

22. 0:
#1
ag
Array Counters
Fl
­ Higher level languages
have no problem
­ Using the number of the print $#array + 1;
last element
­ The number of elements
print scalar @array;

23. 1:
#1
ag
Variable abuse
Fl
­ Are you kidding me? sub calc_ages {
­ Awful awful awful
­ The reasons people get my ( $age1, $age2, $age3,
their hands chopped off in $age4 ) = @_;
indigenous countries
}
calc_ages( $age1, $age2,
$age3, $age4 );

24. 1:
#1
ag
Variable Abuse
Fl
­ That's why we have my @ages = @_;
compound data structures
(arrays, hashes) my %people = (
­ Even more complex data dad => {
structures, if you want
brothers => [],
sisters => [],
},
},
};

25. 2:
#1
ag
C Style for() Loop
Fl
­ Not really an issue for ( $i = 0; $i < 10; $i++ ) {
­ Harder to understand
­ And just not needed …
}

26. 2:
#1
ag
C Style for() Loop
Fl
­ Higher level languages foreach my $var (@vars) {
have better/cooler things
­ foreach (where available) ...
}

27. 3:
#1
ag
Goto Hell
Fl
­ OMGWTF?!1 if ( something_happened() ) {
­ But seriously folks, goto()
strips away all of our ability WHINE: say_it('happened');
to profoundly express my $care = your($feelings);
ourselves using languages
if ( !$care ) {
that finally let us
­ And yes, if you use goto WHINE;
goto(), I also think your }
mother is promiscuous
}

28. 3:
#1
ag
Goto Hell
Fl
­ DON'T USE GOTO! if ( something_happened() ) {
­ You're not a hardcore
assembly programmer, my $care;
you shouldn't have while ( !$care ) {
spaghetti code
say_it('happened');
­ Even xkcd agrees with
me! $care = your($feelings);
}
}

30. ff
tu
s
od Dry, Rinse, Repeat
go
e
m
so
DRY (Don't Repeat Yourself)
Don't duplicate code, abstract it!
KISS (Keep It Simple, Stupid)
Don't write overtly complex stuff. Clean design yields
clean code. (yet some things are complex, I know...)
YAGNI (You Aren't Gonna Need It)
Start from what you need. Work your way up.

31. Thank you.