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At DConf '22 day 3 Robert Schadek presented at around 07:22:00 in the YT video the function splitIds. Given an HTML page from bugzilla containing a list of issues splitIds aims at extracting all bug-ids referenced within a specific url context:
long [] splitIds (string page)
{
enum re = ctRegex!(`"show_bug.cgi\?id=[0-9]+"`);
auto m = page.matchAll (re);
return m
.filter!(it => it.length > 0) // what is this?
.map!(it => it.front) // whole match, it[0]
.map!(it => it.find!(isNumber)) // searches fist number
.map!(it => it.until!(it => !it.isNumber ())) // last number
.filter!(it => !it.empty) // again an empty check??? why?
.map!(it => it.to!long ())
.uniq // .sort is missing. IMHO saving at the wrong things?
.array;
}
m contains all matches. It is a "list of lists" as one would say in Perl. The "inner lists" contains as first element ("front") the string which matches the whole pattern. So my first question is:
What is the purpose of the first filter call? Since the element of m is a match it cannot have a length of 0.
Then the code – and this took me some time to grasp – zooms into the match and tries to match the subexpression which starts with a number and ends with a number. But why does the author not use regular expression subexpression matching [1]? Is that really such an arcane discipline?
Next comes a filter call that seems to defend against the empty string. But there will be no empty string because [0-9]+ only matches if there is at least one number.
Then there is something missing: Before the uniq call there is the assumption that bugzilla ordered the bugs already. What puzzles me is that on the one hand the author puts two find calls into the chain to guard against empty matches which cannot (?) happen but on the other hand ignores that the data may not be sorted. I mean the sortedness is nothing that the author of the function could control.
This is what my version of splitIds looks like:
long [] my_splitIds (string page)
{
enum re = ctRegex!(`"show_bug.cgi\?id=([0-9]+)"`);
auto m = page.matchAll (re);
return m
.map!(it => it[1]) // take the subexpression
.map!(it => it.to!long ())
.array
.sort
.uniq
.array
;
}
For those who ask how one would write such a function in Perl:
sub splitIds ($)
{
my $page = shift;
my @ids = $page =~ m/"show_bug.cgi\?id=([0-9]+)"/g;
my %hash = map { $_ => undef } @ids; # perl has no builtin uniq
sort { $a <=> $b } keys %hash; # force numeric sorting with <=>
}
