Perl 内部结构详解 -- PerlGuts Illustrated (3 AV)

AV

数组，结构如图所示：

字段ALLOC 指向实际分配的SV 数组的开头地址。

字段ARRAY 指向数组本身的开头地址，由于数组的改变，这个地址比起实际分配的地址，可能会产生一定的偏移。

字段FILL 指向数组本身最后一个位置的偏移。

字段MAX 指向分配的SV 数组最后一个位置的偏移。

C:&;perl -MDevel::Peek -e "@a = 1..2; Dump @a"
SV = RV(0x299120) at 0x299114
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x182a9cc
  SV = PVAV(0x29a03c) at 0x182a9cc
    REFCNT = 2
    FLAGS = ()
    ARRAY = 0x1852984
    FILL = 1  (数组最后一个元素index为1)
    MAX = 3   (分配的数组空间最大index为3，说明还有剩余空间来分配)
    ARYLEN = 0x0
    FLAGS = (REAL)
    Elt No. 0
    SV = IV(0x299220) at 0x299224
      REFCNT = 1
      FLAGS = (IOK,pIOK)
      IV = 1
    Elt No. 1
    SV = IV(0x299230) at 0x299234
      REFCNT = 1
      FLAGS = (IOK,pIOK)
      IV = 2

shift pop 操作可以通过调节ARRAY FILL MAX来完成。

C:&;perl -MDevel::Peek -e "@a = 0..3; Dump @a; shift @a; pop @a; Dump @a"
SV = RV(0x299130) at 0x299124
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x182aa14
  SV = PVAV(0x29a04c) at 0x182aa14
    REFCNT = 2
    FLAGS = ()
    ARRAY = 0x1824afc
    FILL = 3
    MAX = 3
    ARYLEN = 0x0
    FLAGS = (REAL)
    Elt No. 0
    SV = IV(0x299280) at 0x299284
      REFCNT = 1
      FLAGS = (IOK,pIOK)
      IV = 0
...
SV = RV(0x2991e0) at 0x2991d4
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x182aa14
  SV = PVAV(0x29a04c) at 0x182aa14
    REFCNT = 2
    FLAGS = ()
    ARRAY = 0x1824b00 (offset=1)
    ALLOC = 0x1824afc
    FILL = 1
    MAX = 2
    ARYLEN = 0x0
    FLAGS = (REAL)
    Elt No. 0
    SV = IV(0x299200) at 0x299204
      REFCNT = 1
      FLAGS = (IOK,pIOK)
      IV = 1
    Elt No. 1
    SV = IV(0x182aa40) at 0x182aa44
      REFCNT = 1
      FLAGS = (IOK,pIOK)
      IV = 2

FLAGS REIFY 表示这个数组不是一个REAL 类型的，当这个数组发生改变的时候需要置为REAL，默认参数@_ 都是使用REIFY 标记。