perl智能匹配

1.perl中~~为智能匹配，它能够智能地依据符号两側的操作数来确定操作。

如要推断某个元素是否存在于数组中，不使用智能匹配，程序像这样：

my $x=2;
my @array=(1,2,3);
my $flag=0;
for (@array)
{
if($x==$_)
{
$flag=1;
}
}

if($flag == 1){
print "$x is in the array";
}
else
{
print "$x is not in the array";
}

使用智能匹配，程序像这样：

my $x=2;
my @array;
if(@array~~$x)
{
print "$x is in the array";
}
else
{
print "$x is in the array";
}

再如查看哈希表中是否存在某个键值

‘hello’~~{hello=>1,world=>2}  结果为true

2.智能匹配的优先级在perl的在线文档中，智能匹配会依照表格的顺序选择匹配，优先级从上到下逐渐减少。

     $a      $b        Type of Match Implied    Matching Cod
    ======  =====     =====================    =============
    Hash    Hash      hash keys identical      [sort keys %$a]~~[sort keys %$b]
    Hash    Array     hash slice existence     grep {exists $a->{$_}} @$b
    Hash    Regex     hash key grep            grep /$b/, keys %$a
    Hash    Any       hash entry existence     exists $a->{$b}

    Array   Array     arrays are identical[*]
    Array   Regex     array grep               grep /$b/, @$a
    Array   Num       array contains number    grep $_ == $b, @$a
    Array   Any       array contains string    grep $_ eq $b, @$a

    Any     undef     undefined                !defined $a
    Any     Regex     pattern match            $a =~ /$b/
    Code()  Code()    results are equal        $a->() eq $b->()
    Any     Code()    simple closure truth     $b->() # ignoring $a
    Num     numish[!] numeric equality         $a == $b
    Any     Str       string equality          $a eq $b
    Any     Num       numeric equality         $a == $b

    Any     Any       string equality          $a eq $b