每当 Perl 需要将值转换为字符串时,就会发生“字符串化”。这可能是打印它、将它与另一个字符串连接、对其应用正则表达式,或者使用 Perl 中的任何其他字符串操作函数。
say $obj;
say "object is: $obj";
if ($obj =~ /xyz/) {...}
say join ', ' => $obj, $obj2, $obj3;
if (length $obj > 10) {...}
$hash{$obj}++;
...
通常,对象会字符串化为类似的东西Some::Package=HASH(0x467fbc)
其中 perl 正在打印它所在的包,以及引用的类型和地址。
某些模块选择覆盖此行为。在 Perl 中,这是通过overload http://perldoc.perl.org/overload.html杂注。下面是一个对象的示例,当字符串化时会产生其总和:
{package Sum;
use List::Util ();
sub new {my $class = shift; bless [@_] => $class}
use overload fallback => 1,
'""' => sub {List::Util::sum @{$_[0]}};
sub add {push @{$_[0]}, @_[1 .. $#_]}
}
my $sum = Sum->new(1 .. 10);
say ref $sum; # prints 'Sum'
say $sum; # prints '55'
$sum->add(100, 1000);
say $sum; # prints '1155'
还有其他几个证明overload
让您定义:
'bool' Boolification The value in boolean context `if ($obj) {...}`
'""' Stringification The value in string context `say $obj; length $obj`
'0+' Numification The value in numeric context `say $obj + 1;`
'qr' Regexification The value when used as a regex `if ($str =~ /$obj/)`
对象甚至可以表现为不同的类型:
'${}' Scalarification The value as a scalar ref `say $$obj`
'@{}' Arrayification The value as an array ref `say for @$obj;`
'%{}' Hashification The value as a hash ref `say for keys %$obj;`
'&{}' Codeification The value as a code ref `say $obj->(1, 2, 3);`
'*{}' Globification The value as a glob ref `say *$obj;`