threads / patch / 12854

patchgitweb: Uniquify usage of subroutine prototypes

Subject: [PATCH] gitweb: Uniquify usage of subroutine prototypes

## tl;dr

3 messages between Mar 25, 2008 and Mar 25, 2008. Diffs are folded; open one to read it.

replies: 2people: 3as markdown or json

Jakub Narebski· Mar 25, 2008, 12:11 UTC · lore

The idea is NOT to use subroutine prototypes to create new syntax; prototypes are to be purely informational and optional. Subroutine prototypes are meant in gitweb to mark untypical parameters, like having hash as an argument, or using hash for last parameter to pass extra options to subroutine.

(Truth to be told this change was caused by the fact that CPerl mode, Perl mode for GNU Emacs, got confused in presence of "sub name($) {" prototype...)

Signed-off-by: Jakub Narebski <jnareb@gmail.com>
---
 gitweb/gitweb.perl |   10 +++++-----
 1 files changed, 5 insertions(+), 5 deletions(-)

Show changes to gitweb/gitweb.perl +5 −5

diff --git a/gitweb/gitweb.perl b/gitweb/gitweb.perl
index ec73cb1..ee5cbd6 100755
--- a/gitweb/gitweb.perl
+++ b/gitweb/gitweb.perl
@@ -587,7 +587,7 @@ exit;
 ## ======================================================================
 ## action links
 
-sub href(%) {
+sub href (%) {
 	my %params = @_;
 	# default is to use -absolute url() i.e. $my_uri
 	my $href = $params{-full} ? $my_url : $my_uri;
@@ -740,7 +740,7 @@ sub esc_html ($;%) {
 }
 
 # quote control characters and escape filename to HTML
-sub esc_path {
+sub esc_path ($;%) {
 	my $str = shift;
 	my %opts = @_;
 
@@ -754,7 +754,7 @@ sub esc_path {
 }
 
 # Make control characters "printable", using character escape codes (CEC)
-sub quot_cec {
+sub quot_cec ($;%) {
 	my $cntrl = shift;
 	my %opts = @_;
 	my %es = ( # character escape codes, aka escape sequences
@@ -780,7 +780,7 @@ sub quot_cec {
 
 # Alternatively use unicode control pictures codepoints,
 # Unicode "printable representation" (PR)
-sub quot_upr {
+sub quot_upr ($;%) {
 	my $cntrl = shift;
 	my %opts = @_;
 
@@ -982,7 +982,7 @@ use constant {
 };
 
 # submodule/subproject, a commit object reference
-sub S_ISGITLINK($) {
+sub S_ISGITLINK {
 	my $mode = shift;
 
 	return (($mode & S_IFMT) == S_IFGITLINK)

-- 
1.5.4.4

Junio C Hamano· Mar 25, 2008, 19:47 UTC · re: Jakub Narebski · lore

Re: [PATCH] gitweb: Uniquify usage of subroutine prototypes

Junio C Hamano <gitster@pobox.com> writes:

> Jakub Narebski <jnareb@gmail.com> writes:
>
>> The idea is NOT to use subroutine prototypes to create new syntax;
>> prototypes are to be purely informational and optional.

That's unfortunately a grave misconception, isn't it?

For example, can you explain (1) how these three calls behave before running them, and (2) why these three behave the way they do?

        sub foo       { my ($s, %f) = @_; print "s = $s\n"; }
        sub bar ($;%) { my ($s, %f) = @_; print "s = $s\n"; }

        my @it = ('This is my string');
        my %hash = (rose => 'blue', violet => 'green');

        foo @it, %hash;		# call 1
        bar @it, %hash;		# call 2
	bar $it[0], %hash;	# call 3

By adding ($;%) to an existing function that did not have prototype, you changed the semantics of the function and:

 (1) it is your responsibility to make sure you did not break existing
     callers when you made such a change, and

 (2) programmers who want to call any existing function in your program
     need to check how the function groks its parameters and make sure
     they do not fall into the same pitfalls as the call sites you had to
     fix in step (1).  They cannot rely on the old fashioned "arguments
     are passed as a flattened list" idiom anymore before checking if you
     have prototypes to the function they want to call.

Prototypes used carelessly tend to force users to do unnecessary things, because the caller cannot rely on the old fashioned "arguments are passed as a flattened list" semantics and check how each and every function is prototyped before making a call.

I am not saying that Perl prototypes is a bad thing. The point of the prototype is to change the syntax and semantics so that you can write a function to which arguments are _not_ passed as a flattend list, and without them you cannot write something that emulates "push @a, $b, $c".

But you need to be aware of what it does to your callers.

Rafael Garcia-Suarez· Mar 25, 2008, 22:06 UTC · re: Junio C Hamano · lore

Re: [PATCH] gitweb: Uniquify usage of subroutine prototypes

On 25/03/2008, Junio C Hamano <junio@pobox.com> wrote:

>  I am not saying that Perl prototypes is a bad thing.  The point of the
>  prototype is to change the syntax and semantics so that you can write a
>  function to which arguments are _not_ passed as a flattend list, and
>  without them you cannot write something that emulates "push @a, $b, $c".

I would agree with what Junio says here. The primary motivation of prototypes was to emulate the syntax of perl built-ins, and their extension (with the _ character) in Perl 5.10 has followed this general principle. As a general rule, I tend to avoid using prototypes for 'normal' functions. That's mostly an application of the least surprise principle.