Perl如何解析未引用的裸词? [英] How does Perl parse unquoted bare words?
问题描述
未引号的单词在Perl中似乎有很多含义.
Unquoted words seem to have a great many meanings in Perl.
print STDERR $msg;
$hash{key}
func( param => $arg )
my $x = str;
如何确定这些含义?
推荐答案
下图显示了Perl如何按优先级降序解析标识符.
The following chart shows how Perl resolves identifiers in order of descending priority.
除非另有说明，否则它也适用于由::链接的标识符(我将其称为合格标识符").
It also applies to identifiers chained by :: (which I'll call "qualified identifiers") unless otherwise stated.
-
在语法上预期的语法上定义的含义.
Syntactically-defined meaning, when syntactically expected.
sub foo { } # «foo» («sub» is covered later)
sub main::foo { } # «main::foo» («sub» is covered later)
method Class # «Class» («method» is covered later)
method Some::Class # «Some::Class» («method» is covered later)
$foo
$main::foo
//i
=head
<<FOO
Class::
Some::Class::
LABEL:
字符串文字，后接=>或整个哈希索引表达式时.
String literal, when followed by a => or when the entirety of a hash index expression.
这不适用于合格的标识符.
my %h = ( a => 1 );
$h{a}
关键字.
Keyword.
while (1) { }
sub { }
BEGIN { }
use
__END__
变量名称，当整个取消引用表达式时.
Variable name, when the entirety of the dereference expression.
${foo}
${main::foo}
请注意，使用命名运算符的名称将导致ambiguous use警告.
Note that using the name of a named operator will result in an ambiguous use warning.
子调用，当先前导入的子名称时使用.
Sub call, when the name of a previously imported sub.
use Time::HiRes qw( time );
time
main::time
调用命名列表运算符，命名一元运算符或命名空运算符.
Invocation of a named list operator, named unary operator or named nullary operator.
print $x, $y, $z;
$c = chr $i;
$t = time;
$t = CORE::time;
标签，当用作next，last，redo或goto的操作数时.
Label, when used as the operand for next, last, redo or goto.
标签不能是合格的标识符，因此它们不被这些运算符接受为操作数.
next LABEL;
子调用或内联常量，如果先前声明了子或常量的名称.
Sub call or inlined constant, when the name of a previously declared sub or constant.
sub foo { }
foo # Calls sub «foo»
main::foo # Calls sub «foo»
sub bar;
bar # Calls sub «bar»
use constant FOO => 123;
FOO # Replaced with the value of the constant.
间接方法调用，后跟一个可能合格的标识符，一个后缀为::的可能合格标识符，标量(包括数组元素或哈希元素)或块.
Indirect method call, when followed by a possibly-qualified identifier, a possibly-qualified identifier suffixed with ::, a scalar (incl array element or hash element) or a block.
method Class # Calls method «method» («Class» is covered earlier)
method Some::Class # Calls method «method» («Some::Class» is covered earlier)
method Class:: # Calls method «method» («Class» is covered earlier)
method Some::Class:: # Calls method «method» («Some::Class» is covered earlier)
method $o # Calls method «method»
method { $o } # Calls method «method»
Base::method Class # Calls method «Base::method» («Class» is covered earlier)
Glob，当用作期望文件句柄的运算符的操作数时.
Glob, when used as the operand for an operator expecting a file handle.
open(FH, '>', $qfn) or die $!; # Equivalent to open(*FH, ...) or ...;
print FH "Hello, World!\n"; # Equivalent to print *FH ...;
print main::FH "Hello, World!\n"; # Equivalent to print *main::FH ...;
字符串文字，在以下情况下:
String literal, in the following situations:
-
用作直接方法调用的倡导者.
When used as the invocant of a direct method call.
Class->method(@args) # Uses the string «Class» as the invocant.
Some::Class->method(@args) # Uses the string «Some::Class» as the invocant.
用作一元减的操作数.
When used as the operand for unary minus.
-foo
-foo::bar
当用作带有*原型的sub参数的参数时.
When used as an argument for the a sub parameter with a prototype of *.
sub myprint(*@);
myprint(FH, "Hello, World\n");
myprint(main::FH, "Hello, World\n");
字符串文字. use strict qw( subs );不允许这样做.
String literal. This is disallowed by use strict qw( subs );.
希望我没有错过任何机会.
Hopefully, I didn't miss any.
感谢@ mosvy，@ Grinnz和@stevesliva！每个人都发现了我错过的一些情况.
Thanks to @mosvy, @Grinnz and @stevesliva! Each has uncovered a few cases I had missed.
当前丢失:
-
funcname.
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