Question

my $EMPTY = q{};
use constant TRUE  => ( 1==1 );
use constant FALSE => ( 1==2 );


my $a = "";   vs my $a = $EMPTY;             
my $b = 0;    vs my $b = FALSE

对于什么应该使用哪个有什么区别？
这取决于某些情况吗？
如果是这样，那么您希望何时使用my $b = 0;超过my $b = FALSE，反之亦然的情况是什么？

Answer 1

""和q{}都生成零长度字符串。

>perl -MDevel::Peek -e"$_ = q{}; Dump($_);"
SV = PV(0x306748) at 0x4c9058
  REFCNT = 1
  FLAGS = (POK,pPOK)            <--- Contains a string.
  PV = 0x4ac9e8 ""\0
  CUR = 0                       <--- Length of the string is zero.
  LEN = 16

0生成数字零。

>perl -MDevel::Peek -e"$_ = 0; Dump($_)"
SV = IV(0x229088) at 0x229098
  REFCNT = 1
  FLAGS = (IOK,pIOK)            <--- Contains a signed integer.
  IV = 0                        <--- Contained integer is zero.

(1==2)生成一个包含空字符串且数值为零的标量。

>perl -MDevel::Peek -e"$_ = 1==2; Dump($_);"
SV = PVNV(0x1fc598) at 0x259038
  REFCNT = 1
  FLAGS = (IOK,NOK,POK,pIOK,pNOK,pPOK)   <--- A signed int, a float and a str.
  IV = 0                        <--- Contained integer is zero.
  NV = 0                        <--- Contained floating point number is zero.
  PV = 0x23ca18 ""\0
  CUR = 0                       <--- Length of the string is zero.
  LEN = 16

Answer 2

您创建的FALSE值是Perl中特殊PL_sv_no变量的副本。此值在数字上为零且为空状态时是唯一的，并且使用==和eq运算符进行比较时不会发出警告。相比之下，由""或q{}创建的普通空字符串将生成==

的警告

Perl初始化值：“”vs q {}和0 vs（1 == 2）

2 个答案: