Lightning talk given at YAPC::EU 2012

1. ( ) versus ,
Damien Krotkine ( dams )

2. Parens versus Comma

3. Parens versus Comma
or, what people say...

4. Parens versus Comma
or, what people say...
or, a lame excuse to play with Keynote’s effects...

5. my @array = ( 1, 2, 3 )

6. my @array = ( 1, 2, 3 )

7. my @array = ( 1, 2, 3 )

8. my @array = ( 1, 2, 3 )
( 1, 2, 3 )
That’s a list, right ?

9. my @array = ( 1, 2, 3 )
( 1, 2, 3 )
That’s a list, right ?
But what makes it a list ?

10. People say
“ Oh that’s the parens”
“ The parentheses make it a list”

11. People say
“ Oh that’s the parens”
“ The parentheses make it a list”
People also say :
“ See, if you remove the parentheses, it doesn’t
work”

12. my @array = (1, 2, 3);
say “@array” # returns 1 2 3
Yay !

13. my @array = 1, 2, 3 ;
say “@array” # returns 1
Booh !

14. So people say
“ So, it must be the parentheses”
So now people say :
“parentheses are the list operator in Perl 5”

15. I say :
“Oh really ? ”

17. Let’s see... operators, what’s the list of Perl
operators ?

18. Let’s see... operators, what’s the list of Perl
operators ?
man perlop

20. -> &
++ -- | ^
** &&
! ~ + - || //
=~ !~ .. ...
* / % x ?:
+ - . = += -= *= etc.
<< >> , =>
< > <= >= lt gt le ge not
== != <=> eq ne cmp ~~ and
xor

21. -> &
++ -- | ^
** &&
! ~ + - || //
=~ !~ .. ...
* / % x ?:
+ - . = += -= *= etc.
<< >> , =>
< > <= >= lt gt le ge not
== != <=> eq ne cmp ~~ and
xor
There is no ( ) operator

22. -> &
++ -- | ^
** &&
! ~ + - || //
=~ !~ .. ...
* / % x ?:
+ - . = += -= *= etc.
<< >> , =>
< > <= >= lt gt le ge not
== != <=> eq ne cmp ~~ and
xor
There is no ( ) operator

23. -> &
++ -- | ^
** &&
! ~ + - || //
=~ !~ .. ...
* / % x ?:
+ - . = += -= *= etc.
<< >> , =>
< > <= >= lt gt le ge not
== != <=> eq ne cmp ~~ and
xor
There is no ( ) operator
However there is a comma operator

24. -> &
++ -- | ^
** &&
! ~ + - || //
=~ !~ .. ...
* / % x ?:
+ - . = += -= *= etc.
<< >> , =>
< > <= >= lt gt le ge not
== != <=> eq ne cmp ~~ and
xor
There is no ( ) operator
However there is a comma operator
, That’s the operator

25. The comma operator has a very low
precedence, but it’s still an operator
Parentheses ( ) are just there to modify
precedence

27. ( 1, 2, 3 ) is a list

28. ( 1, 2, 3 ) is a list
1, 2, 3 is also a list

30. my @list = 1, 2, 3

31. my @list = 1, 2, 3
So why doesn’t this work ?

32. my @list = 1, 2, 3
So why doesn’t this work ?
That’s because = has greater precedence
than ,

34. my @array = 1, 2, 3;

35. my @array = 1, 2, 3;
is really

36. my @array = 1, 2, 3;
is really
(my @array = 1), 2, 3;

37. my @array = 1, 2, 3;
is really
(my @array = 1), 2, 3;

39. And it’s also

40. And it’s also
( (my @array = 1), 2, 3 );

41. And it’s also
( (my @array = 1), 2, 3 );
So it’s really a list ! We are just not looking
at it completely when looking at @array

42. Why is it useful to know ?

43. It makes you realize you don’t need ( ) in
many situations

45. return 1, 2, 3;

46. return 1, 2, 3;
do_stuff or log(“error”), die;

47. return 1, 2, 3;
do_stuff or log(“error”), die;
my $self = bless { }, $class;

48. return 1, 2, 3;
do_stuff or log(“error”), die;
my $self = bless { }, $class;
etc.

49. return 1, 2, 3;
do_stuff or log(“error”), die;
my $self = bless { }, $class;
etc.
btw this doesn’t work

50. return 1, 2, 3;
do_stuff or log(“error”), die;
my $self = bless { }, $class;
etc.
btw this doesn’t work
do_stuff || log(“error”), die;

51. return 1, 2, 3;
do_stuff or log(“error”), die;
my $self = bless { }, $class;
etc.
btw this doesn’t work
do_stuff || log(“error”), die;
=> go learn your operators’ precedence

52. So please don’t say that ( ) is the Perl 5 list
operator: it is not
Give more love to the comma operator,
it’s often forgotten

53. So please don’t say that ( ) is the Perl 5 list
operator: it is not
Give more love to the comma operator,
it’s often forgotten
♥

54. So please don’t say that ( ) is the Perl 5 list
operator: it is not
Give more love to the comma operator,
it’s often forgotten
♥
And don’t listen to what people say...

55. Thanks
Damien Krotkine ( dams )