如何在 Perl 中修补实例方法? [英] How can I monkey-patch an instance method in Perl?

问题描述

我正在尝试修补 (duck-punch :-) LWP::UserAgent 实例，如下所示:

I'm trying to monkey-patch (duck-punch :-) a LWP::UserAgent instance, like so:

sub _user_agent_get_basic_credentials_patch {
  return ($username, $password);
}

my $agent = LWP::UserAgent->new();
$agent->get_basic_credentials = _user_agent_get_basic_credentials_patch;

这不是正确的语法——它会产生:

This isn't the right syntax -- it yields:

不能修改非左值子程序在 [module] 行 [lineno] 调用.

Can't modify non-lvalue subroutine call at [module] line [lineno].

我记得(来自 Programming Perl)，调度查找是基于受祝福的包动态执行的(ref($agent)，我相信)，所以我我不确定实例猴子补丁如何在不影响祝福包的情况下工作.

As I recall (from Programming Perl), dispatch lookup is performed dynamically based on the blessed package (ref($agent), I believe), so I'm not sure how instance monkey patching would even work without affecting the blessed package.

我知道我可以对 UserAgent 进行子类化，但我更喜欢更简洁的猴子补丁方法.同意成年人和你有什么.;-)

I know that I can subclass the UserAgent, but I would prefer the more concise monkey-patched approach. Consenting adults and what have you. ;-)

推荐答案

如果动态范围(使用local)不令人满意，您可以自动化自定义包reblessing技术:

If dynamic scope (using local) isn't satisfactory, you can automate the custom package reblessing technique:

MONKEY_PATCH_INSTANCE:
{
  my $counter = 1; # could use a state var in perl 5.10

  sub monkey_patch_instance
  {
    my($instance, $method, $code) = @_;
    my $package = ref($instance) . '::MonkeyPatch' . $counter++;
    no strict 'refs';
    @{$package . '::ISA'} = (ref($instance));
    *{$package . '::' . $method} = $code;
    bless $_[0], $package; # sneaky re-bless of aliased argument
  }
}

示例用法:

package Dog;
sub new { bless {}, shift }
sub speak { print "woof!
" }

...

package main;

my $dog1 = Dog->new;
my $dog2 = Dog->new;

monkey_patch_instance($dog2, speak => sub { print "yap!
" });

$dog1->speak; # woof!
$dog2->speak; # yap!

这篇关于如何在 Perl 中修补实例方法?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！