【发布时间】：2011-02-23 06:44:18
【问题描述】：
我目前正在记录 Perl 5 的所有运算符（请参阅perlopref GitHub 项目），并且我决定也包括 Perl 5 的伪运算符。对我来说，Perl 中的伪运算符是任何看起来像运算符的东西，但实际上不仅仅是一个运算符或某种其他语法。我已经记录了我熟悉的四个：
-
()=countof 运算符 -
=()=goatse/countof 运算符 -
~~标量上下文运算符 -
}{爱斯基摩亲吻操作员
这些伪算子还有哪些其他名称，你知道我遗漏了哪些伪算子吗？
=head1 Pseudo-operators
There are idioms in Perl 5 that appear to be operators, but are really a
combination of several operators or pieces of syntax. These pseudo-operators
have the precedence of the constituent parts.
=head2 ()= X
=head3 Description
This pseudo-operator is the list assignment operator (aka the countof
operator). It is made up of two items C<()>, and C<=>. In scalar context
it returns the number of items in the list X. In list context it returns an
empty list. It is useful when you have something that returns a list and
you want to know the number of items in that list and don't care about the
list's contents. It is needed because the comma operator returns the last
item in the sequence rather than the number of items in the sequence when it
is placed in scalar context.
It works because the assignment operator returns the number of items
available to be assigned when its left hand side has list context. In the
following example there are five values in the list being assigned to the
list C<($x, $y, $z)>, so C<$count> is assigned C<5>.
my $count = my ($x, $y, $z) = qw/a b c d e/;
The empty list (the C<()> part of the pseudo-operator) triggers this
behavior.
=head3 Example
sub f { return qw/a b c d e/ }
my $count = ()= f(); #$count is now 5
my $string = "cat cat dog cat";
my $cats = ()= $string =~ /cat/g; #$cats is now 3
print scalar( ()= f() ), "\n"; #prints "5\n"
=head3 See also
L</X = Y> and L</X =()= Y>
=head2 X =()= Y
This pseudo-operator is often called the goatse operator for reasons better
left unexamined; it is also called the list assignment or countof operator.
It is made up of three items C<=>, C<()>, and C<=>. When X is a scalar
variable, the number of items in the list Y is returned. If X is an array
or a hash it it returns an empty list. It is useful when you have something
that returns a list and you want to know the number of items in that list
and don't care about the list's contents. It is needed because the comma
operator returns the last item in the sequence rather than the number of
items in the sequence when it is placed in scalar context.
It works because the assignment operator returns the number of items
available to be assigned when its left hand side has list context. In the
following example there are five values in the list being assigned to the
list C<($x, $y, $z)>, so C<$count> is assigned C<5>.
my $count = my ($x, $y, $z) = qw/a b c d e/;
The empty list (the C<()> part of the pseudo-operator) triggers this
behavior.
=head3 Example
sub f { return qw/a b c d e/ }
my $count =()= f(); #$count is now 5
my $string = "cat cat dog cat";
my $cats =()= $string =~ /cat/g; #$cats is now 3
=head3 See also
L</=> and L</()=>
=head2 ~~X
=head3 Description
This pseudo-operator is named the scalar context operator. It is made up of
two bitwise negation operators. It provides scalar context to the
expression X. It works because the first bitwise negation operator provides
scalar context to X and performs a bitwise negation of the result; since the
result of two bitwise negations is the original item, the value of the
original expression is preserved.
With the addition of the Smart match operator, this pseudo-operator is even
more confusing. The C<scalar> function is much easier to understand and you
are encouraged to use it instead.
=head3 Example
my @a = qw/a b c d/;
print ~~@a, "\n"; #prints 4
=head3 See also
L</~X>, L</X ~~ Y>, and L<perlfunc/scalar>
=head2 X }{ Y
=head3 Description
This pseudo-operator is called the Eskimo-kiss operator because it looks
like two faces touching noses. It is made up of an closing brace and an
opening brace. It is used when using C<perl> as a command-line program with
the C<-n> or C<-p> options. It has the effect of running X inside of the
loop created by C<-n> or C<-p> and running Y at the end of the program. It
works because the closing brace closes the loop created by C<-n> or C<-p>
and the opening brace creates a new bare block that is closed by the loop's
original ending. You can see this behavior by using the L<B::Deparse>
module. Here is the command C<perl -ne 'print $_;'> deparsed:
LINE: while (defined($_ = <ARGV>)) {
print $_;
}
Notice how the original code was wrapped with the C<while> loop. Here is
the deparsing of C<perl -ne '$count++ if /foo/; }{ print "$count\n"'>:
LINE: while (defined($_ = <ARGV>)) {
++$count if /foo/;
}
{
print "$count\n";
}
Notice how the C<while> loop is closed by the closing brace we added and the
opening brace starts a new bare block that is closed by the closing brace
that was originally intended to close the C<while> loop.
=head3 Example
# count unique lines in the file FOO
perl -nle '$seen{$_}++ }{ print "$_ => $seen{$_}" for keys %seen' FOO
# sum all of the lines until the user types control-d
perl -nle '$sum += $_ }{ print $sum'
=head3 See also
L<perlrun> and L<perlsyn>
=cut
【问题讨论】：
-
在旁注中，恕我直言，爱斯基摩人的吻很有趣 XD
-
+=、-=、/=、*=、**=家族和短路运算符||= or //=怎么样？它们是伪操作吗？ -
@klex 是的，一旦你看到它，你就无法取消它。有点像联邦快递中的箭头。 goatse 操作员也是如此，但这不太令人愉快。
-
@Zaid 是的，我已经拥有了 perlop 中的所有内容以及 perlfunc 中记录的文件测试（尽管它们目前只是占位符）。我在这里追求的是看起来像运算符的习语。该项目的用途之一是 Padre Perl IDE 中的上下文相关帮助。这个想法是你按下 F1 并且光标下的任何字符串都与所有 Perl 函数和运算符进行模糊匹配。
-
@Shaggy Frog 啊，你以为我命名了操作员；我没有，我只是在记录使用情况。这就是它的名字。尝试谷歌搜索：google.com/search?q=goatse+operator