Perl初始化值:""vs q {}和0 vs(1 == 2)

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

应该使用哪种方法有什么区别？
这取决于某些情况吗？
如果是这样的话,那些关于何时想要使用的my $b = 0;情况my $b = FALSE又是什么呢？反之亦然？

Answer 1

• ""并且q{}都产生零长度的字符串.

  >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 产生数字零.

  >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) 生成标量包含空字符串,数值为零.

  >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