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新手求助perl智能匹配

时间：2011-07-13

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my @nums = qw( 2  3  42 27 );
my $result = max( @nums );

sub max{
  my ($max_so_far) = shift @_;
  foreach( @_ ) {
  if ($_ > $max_so_far ){
$max_so_far = $_;
}
}
  return $max_so_far;
print "$max_so_far\n";
}
print "the values is existed\n" if $result ~~ @nums;

print "the values is existed\n" if @nums ~~ $result;
为什么按照第二个print语句写没有运行结果，第一个print的运行结果是对的；可书上说智能匹配对两边操作数的顺序没有要求。这两种写法应该有同样的运行结果才对，可实际结果不对。

还有我打印result的值的时候应该是42，怎么输出结果是1啊？

请高手帮忙！谢谢

作者: stesting 发布时间: 2011-07-13

QUOTE:

my @nums = qw( 2 3 42 27 );
my $result = max( @nums );

sub max{
my ($max_so_far) = shift @_ ...
stesting 发表于 2011-07-13 14:39

你的书过时了可书上说智能匹配对两边操作数的顺序没有要求。这一点 5.10.1 改变了

作者: zhlong8 发布时间: 2011-07-13

http://perldoc.perl.org/perlsyn.html#Switch-statements
往下稍微翻一点有个表，用 ~~ 要看这里

QUOTE:

$a    $b       Type of Match Implied Matching Code
======  =====    ===================== =============
Any    undef    undefined             !defined $a
Any    Object invokes ~~ overloading on $object, or dies
Hash CodeRef sub truth for each key[1] !grep { !$b->($_) } keys %$a
Array CodeRef sub truth for each elt[1] !grep { !$b->($_) } @$a
Any    CodeRef scalar sub truth       $b->($a)
Hash Hash    hash keys identical (every key is found in both hashes)
Array Hash    hash keys intersection grep { exists $b->{$_} } @$a
Regex Hash    hash key grep          grep /$a/, keys %$b
undef Hash    always false (undef can't be a key)
Any    Hash    hash entry existence    exists $b->{$a}
Hash Array    hash keys intersection grep { exists $a->{$_} } @$b
Array Array    arrays are comparable[2]
Regex Array    array grep             grep /$a/, @$b
undef Array    array contains undef    grep !defined, @$b
Any    Array    match against an array element[3]
                                             grep $a ~~ $_, @$b
Hash Regex    hash key grep          grep /$b/, keys %$a
Array Regex    array grep             grep /$b/, @$a
Any    Regex    pattern match          $a =~ /$b/
Object  Any    invokes ~~ overloading on $object, or falls back:
Any    Num    numeric equality       $a == $b
Num    numish[4] numeric equality       $a == $b
undef Any    undefined             !defined($b)
Any    Any    string equality       $a eq $b
1 - empty hashes or arrays will match.
2 - that is, each element smart-matches the element of same index in the
   other array. [3]
3 - If a circular reference is found, we fall back to referential equality.
4 - either a real number, or a string that looks like a number

作者: zhlong8 发布时间: 2011-07-13

新手求助perl智能匹配

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