perl – 内置内联的文档？

发布时间：2020-12-15 22:00:04 所属栏目：大数据来源：网络整理

导读：我遇到一种情况,我不能以直观的方式禁止警告,因为perl内置了一个内置函数的调用.例如 use strict;use warnings;{ no warnings 'substr'; # no effect foo(substr('123',4,6)); # out of range but shouldn't emit a warning}sub foo { my $s = shift; # warn

我遇到一种情况,我不能以直观的方式禁止警告,因为perl内置了一个内置函数的调用.例如

use strict;
use warnings;

{
    no warnings 'substr';      # no effect
    foo(substr('123',4,6));  # out of range but shouldn't emit a warning
}

sub foo {
    my $s = shift;  # warning reported here
    # do something
}

运行此代码导致

substr outside of string at c:tempfoo.pl line 10.

为了禁止警告,我必须在函数内移动no warnings’substr’.

sub foo {
    no warnings 'substr'; # works here,but there's no call to substr
    my $s = shift;        # no warnings here
    # do something
}

我可以看到,通过传递代码通过perl -MO = Terse来调用substr是内联的

LISTOP (0x27dcaa8) leave [1]
    OP (0x27a402c) enter
    COP (0x27dcac8) nextstate
    BINOP (0x27dcb00) leaveloop
        LOOP (0x27dcb20) enterloop
        LISTOP (0x27dcb68) lineseq
            COP (0x27dcb88) nextstate
            UNOP (0x27dcbc0) entersub [5]          # entry point for foo
                UNOP (0x27dcbf4) null [148]
                    OP (0x27dcbdc) pushmark
                    LISTOP (0x27dcc48) substr [4]  # substr gets called here
                        OP (0x27dcc30) null [3]
                        SVOP (0x27dcc84) const [6] PV (0x2319944) "123"
                        SVOP (0x27dcc68) const [7] IV (0x2319904) 4
                        SVOP (0x27dcc14) const [8] IV (0x231944c) 6
                    UNOP (0x27dcca0) null [17]
                        PADOP (0x27dccf4) gv  GV (0x2318e5c) *foo

这个优化器行为是否记录在任何地方？ perlsub只提到不断的功能内联.鉴于警告正在以错误的方式报告,并且在呼叫的词汇范围内没有警告不起作用,因此我倾向于将其作为错误报告,尽管我不能想到如何合理地固定,同时保持优化.

注意：在Perl 5.16.1中观察到这种情况.

解决方法

正如你从B :: Terse看到的,substr不是内联的.

$perl -MO=Concise,-exec -e'f(substr($_,3,4))'
1  <0> enter
2  <;> nextstate(main 1 -e:1) v:{
3  <0> pushmark s
4  <#> gvsv[*_] s
5  <$> const[IV 3] s
6  <$> const[IV 4] s
7  <@> substr[t4] sKM/3        <-- The substr operator is evaluated first.
8  <#> gv[*f] s/EARLYCV
9  <1> entersub[t5] vKS/TARG   <-- The sub call second.
a  <@> leave[1 ref] vKP/REFC
-e syntax OK

当substr被称为左值上下文时,substr返回一个包含传递给substr的操作数的神奇标量.

$perl -MDevel::Peek -e'$_ = "abcdef"; Dump(${ substr($_,4) })'
SV = PVLV(0x2865d60) at 0x283fbd8
  REFCNT = 2
  FLAGS = (GMG,SMG)          <--- Gets and sets are magical.
  IV = 0                          GMG: A function that mods the scalar
  NV = 0                               is called before fetches.
  PV = 0                          SMG: A function is called after the
  MAGIC = 0x2856810                    scalar is modified.
    MG_VIRTUAL = &PL_vtbl_substr
    MG_TYPE = PERL_MAGIC_substr(x)
  TYPE = x
  TARGOFF = 3                      <--- substr's second arg
  TARGLEN = 4                      <--- substr's third arg
  TARG = 0x287bfd0                 <--- substr's first arg
  FLAGS = 0              
  SV = PV(0x28407f0) at 0x287bfd0  <--- A dump of substr's first arg
    REFCNT = 2
    FLAGS = (POK,IsCOW,pPOK)
    PV = 0x2865d20 "abcdef"
    CUR = 6
    LEN = 10
    COW_REFCNT = 1

子例程参数在lvalue上下文中进行求值,因为Perl [1]中的子程序参数始终通过引用传递.

$perl -E'sub f { $_[0] = "def"; }  $x = "abc"; f($x); say $x;'
def

当访问魔法标量时,发生子串操作.

$perl -E'$x = "abc"; $r = substr($x,1); $x = "def"; say $$r;'
d

这样做可以让substr(…)=“abc”;

>这可能是使用类似于以下的语言记录的：“@_的元素被别名到子例程参数.

（编辑：李大同）

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