Question

Perl中my ($variableName)和my $variableName之间有什么区别？括号怎么办？

Answer 1

重要的效果是在声明变量的同时初始化变量：

my ($a) = @b;   # assigns  $a = $b[0]
my $a = @b;     # assigns  $a = scalar @b (length of @b)

另一个重要的是当你声明多个变量时。

my ($a,$b,$c);  # correct, all variables are lexically scoped now
my $a,$b,$c;    # $a is now lexically scoped, but $b and $c are not

如果您use strict，最后一条语句会给您一个错误。

Answer 2

有关my运算符的详细信息，请查看perdoc perlsub。这是一个小摘录：

梗概：

   my $foo;            # declare $foo lexically local
   my (@wid, %get);    # declare list of variables local
   my $foo = "flurp";  # declare $foo lexical, and init it
   my @oof = @bar;     # declare @oof lexical, and init it
   my $x : Foo = $y;   # similar, with an attribute applied

Answer 3

简短的回答是，在=的左侧使用括号时强制列表上下文。

其他每个答案都指出了一个特殊情况，这会产生影响。实际上，您应该通读perlfunc以更好地了解函数在列表上下文中调用时的行为方式，而不是标量上下文。

Answer 4

正如另一个答案和评论所解释，括号的用法为变量提供了列表上下文。下面是一段代码片段，它通过使用perl函数split提供了更多解释



use strict;

my $input = "one:two:three:four";

# split called in list context
my ($out) = split(/:/,$input);
# $out contains string 'one' 
#(zeroth element of the list created by split operation)
print $out,"\n";

# split called in scalar context
my $new_out = split(/:/,$input);
# $new_out contains 4 (number of fields found)
print $new_out,"\n";

use strict; my $input = "one:two:three:four"; # split called in list context my ($out) = split(/:/,$input); # $out contains string 'one' #(zeroth element of the list created by split operation) print $out,"\n"; # split called in scalar context my $new_out = split(/:/,$input); # $new_out contains 4 (number of fields found) print $new_out,"\n";

我的（$变量名称）和我的$变量名称在Perl中有什么区别？

4 个答案: