Perl 5中存在哪些伪操作符?

我目前正在logging所有的Perl 5的操作符(请参阅perlopref GitHub项目),我也决定包含Perl 5的伪操作符。 对我来说,Perl中的伪操作符是任何看起来像操作符的东西,但实际上不止一个操作符或其他一些语法。 我已经logging了我已经熟悉的四个:

  • ()=运算符的个数
  • =()= goatse / countof操作符
  • 标量上下文运算符
  • }{爱斯基摩人接吻操作员

这些伪操作符还有其他什么名字,你知道我错过的伪操作吗?

 =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/abcde/; The empty list (the C<()> part of the pseudo-operator) triggers this behavior. =head3 Example sub f { return qw/abcde/ } 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/abcde/; The empty list (the C<()> part of the pseudo-operator) triggers this behavior. =head3 Example sub f { return qw/abcde/ } 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/abcd/; 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 

9 Solutions collect form web for “Perl 5中存在哪些伪操作符?”

漂亮的项目,这里有几个:

 scalar x!! $value # conditional scalar include operator (list) x!! $value # conditional list include operator 'string' x/pattern/ # conditional include if pattern "@{[ list ]}" # interpolate list expression operator "${\scalar}" # interpolate scalar expression operator !! $scalar # scalar -> boolean operator +0 # cast to numeric operator .'' # cast to string operator { ($value or next)->depends_on_value() } # early bail out operator # aka using next/last/redo with bare blocks to avoid duplicate variable lookups # might be a stretch to call this an operator though... sub{\@_}->( list ) # list capture "operator", like [ list ] but with aliases 

在Perl中,这些通常被称为“秘密操作员”。

这里可以列出部分“秘密操作员”。 最好和最完整的名单可能是拥有菲利普Bruhad又名BooK和他的秘密Perl运算符谈话,但我不知道它可用。 你可能会问他。 你也许可以从迷惑,高尔夫和秘密运营商那里收集更多。

不要忘记火焰X翼 =<>=~

与Perl的邮件列表的乐趣将certificate对你的研究有用。

“去”和“接近”运营商:

 $x = 10; say $x while $x --> 4; # prints 9 through 4 $x = 10; say $x while 4 <-- $x; # prints 9 through 5 

它们不是Perl独有的。

从这个问题中 ,我发现%{{}}运算符将一个列表作为一个散列。 在需要散列参数(而不是散列分配)的上下文中很有用。

 @list = (a,1,b,2); print values @list; # arg 1 to values must be hash (not array dereference) print values %{@list} # prints nothing print values (%temp=@list) # arg 1 to values must be hash (not list assignment) print values %{{@list}} # success: prints 12 

如果@list不包含任何重复的键(奇数元素),该运算符还提供了访问列表的奇数或偶数元素的方法:

 @even_elements = keys %{{@list}} # @list[0,2,4,...] @odd_elements = values %{{@list}} # @list[1,3,5,...] 

Perl秘密操作员现在对CPAN有一些参考(几乎是官方的,但它们是“秘密的”)文档: perlsecret

你有两个“伪”操作符,我真的不知道它们之间的区别。

从“算数算子”的例子来看:

 my $count = ()= f(); #$count is now 5 my $string = "cat cat dog cat"; my $cats = ()= $string =~ /cat/g; #$cats is now 3 

从“山羊/算子”的例子来看:

 my $count =()= f(); #$count is now 5 my $string = "cat cat dog cat"; my $cats =()= $string =~ /cat/g; #$cats is now 3 

两组示例都是相同的,模空白。 你认为他们是两个不同的伪操作员的理由是什么?

“布尔一或零”运算符如何? 1&!!

例如:

 my %result_of = ( " 1&!! '0 but true' " => 1&!! '0 but true', " 1&!! '0' " => 1&!! '0', " 1&!! 'text' " => 1&!! 'text', " 1&!! 0 " => 1&!! 0, " 1&!! 1 " => 1&!! 1, " 1&!! undef " => 1&!! undef, ); for my $expression ( sort keys %result_of){ print "$expression = " . $result_of{$expression} . "\n"; } 

给出以下输出:

  1&!! '0 but true' = 1 1&!! '0' = 0 1&!! 'text' = 1 1&!! 0 = 0 1&!! 1 = 1 1&!! undef = 0 

<< >>操作符,用于多行注释 :

 <<q==q>>; This is a multiline comment q 
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