zhengpd (Zheng Piaodan)

启用 chrome custom doh 打不开 ruby china

zhengpd — Fri, 24 Dec 2021 19:34:27 +0800

如图，Chrome 如果启用 Secure DNS 和用自定义的 doh，就打不开 ruby-china.org，不知道其他人有没有这个问题

tmux + nvim 的 pane/window 快速切换

zhengpd — Thu, 05 Aug 2021 22:25:57 +0800

tmux + nvim 的 pane/window 快速切换

缘由

13 寸的屏幕有点小，所以 tmux 一般是多用 window 少用 pane，至少一个放 neovim 一个跑 zsh，来回切 window 多了觉得 <prefix> l 或者 <prefix> h这样的组合键还是有点繁琐。之前一直是用 vim-tmux-navigator 做 tmux pane 之间的切换，于是就想着能不能把 <C-l> 也绑到 tmux window 切换上去。由于 vim-tmux-navigator 不支持 tmux window，只能自己搞了个配置，分享给有类似需求的朋友看下。

逻辑比较简单，以 <C-l> 为例：

当前为 nvim 左边 window
<C-l> 切到 nvim 右边 window
再 <C-l> 一下切到右边的 tmux pane
再 <C-l> 一下切到下一个 tmux window

配置

vim conf:

" ~/.vimrc
function! TmuxWinJump(direction)
  let direction_edges = {
        \ 'h': 'pane_at_left',
        \ 'j': 'pane_at_bottom',
        \ 'k': 'pane_at_top',
        \ 'l': 'pane_at_right'
        \}

  let edge_cmd = 'tmux display-message -p "#{'.direction_edges[a:direction].'}"'
  if trim(system(edge_cmd)) == 1
    let tmux_direction = { 'h': '-', 'j': '+', 'k': '-', 'l': '+' }
    call system('tmux select-window -t :'.tmux_direction[a:direction])
  else
    let pane_direction = tr(a:direction, 'hjkl', 'LDUR')
    call system('tmux select-pane -'.pane_direction)
  endif
endfunction

function! VimWinJump(direction)
  let nr = winnr()
  exec 'wincmd '.a:direction

  if winnr() == nr | call TmuxWinJump(a:direction) | endif
endfunction

nnoremap <silent> <C-h> :call VimWinJump('h')<cr>
nnoremap <silent> <C-j> :call VimWinJump('j')<cr>
nnoremap <silent> <C-k> :call VimWinJump('k')<cr>
nnoremap <silent> <C-l> :call VimWinJump('l')<cr>

tmux conf:

~/.tmux.conf
is_nvim='tmux list-panes -F "#{l:#{pane_current_command}} #{l:#{pane_id}}" | grep #{pane_id} | grep -iqE "nvim|fzf"'

h_handler='if -F  "#{pane_at_left}" "select-window -t :-" "select-pane -L"'
bind-key -n 'C-h' if-shell "$is_nvim" 'send-keys C-h' "$h_handler"

j_handler='if -F  "#{pane_at_bottom}" "select-window -t :+" "select-pane -D"'
bind-key -n 'C-j' if-shell "$is_nvim" 'send-keys C-j' "$j_handler"

k_handler='if -F  "#{pane_at_top}" "select-window -t :-" "select-pane -U"'
bind-key -n 'C-k' if-shell "$is_nvim" 'send-keys C-k' "$k_handler"

l_handler='if -F  "#{pane_at_right}" "select-window -t :+" "select-pane -R"'
bind-key -n 'C-l' if-shell "$is_nvim" 'send-keys C-l' "$l_handler"

Credits

Inspired by https://github.com/christoomey/vim-tmux-navigator

【建议】关于删除最后回复后的贴子列表排序

zhengpd — Sat, 30 May 2020 17:46:49 +0800

目前如果一个贴子的最后回复被删除，这个贴子会被认为有了新动态从而排序在贴子列表的前面。

建议 topic.last_active_mark 在贴子有回复的情况下不用 Time.now 而是用 reply.created_at，跟最后一条未删除回复的创建时间绑定。

Demystify Ruby Class Variables Lookup

zhengpd — Thu, 19 Mar 2020 01:22:22 +0800

发帖前言

在社区看到一个类变量查询问题的帖子，做了些关于 Ruby 类变量查找的研究。如有错误，欢迎指正。

Demystify Ruby Class Variables Lookup

Zheng Piaodan @ 2020-03-19

Preface

A post caught my attention recently. It's at https://ruby-china.org/topics/39618. It's about class variables collecting and lookup in Ruby. And I decided to find out what's happening under the hood.

Issue Description

See how class_variables and class_variable_get behave differently in sample:

module Foo; @@foo = 'foo'; end
class Bar; extend Foo; end

RUBY_VERSION
# => "2.6.5"
Bar.class_variables
# => []
Bar.singleton_class.class_variables 
# => [:@@foo]
Bar.singleton_class.class_variable_get(:@@foo) 
# NameError (uninitialized class variable @@foo in #<Class:Bar>)
Bar.singleton_class.singleton_class.class_variable_get(:@@foo) 
# => "foo"

Details Investigation

NOTE: all code analyses are based on Ruby 2.6.5 if ruby version not specified.

The issue was reported back in 2013 at https://bugs.ruby-lang.org/issues/8297.
Jeremy Evans made a fix in 2019, merged in Ruby 2.7.0, at https://github.com/ruby/ruby/pull/2478.
In our case here, Evans' fix makes Bar.singleton_class.class_variables returns [] instead of [:@@name].

How extend method works

In short, ruby's extend puts module as direct ancestor to the singleton class of current class, while include puts module as direct ancestor to current class.

In long, I don't have the long story right now...I'll tell you all about it when I dig it again.

How class_variables method works

Let ST = Bar.singleton_class for convenience.

Ruby 2.6.5 behavior

For Ruby 2.6, when Bar.class_variables or ST.class_variablesis called, Ruby will collect class variables defined on:

receiver itself , Bar or ST
receivers' ancestors , Bar.ancestors or ST.ancestors

Normal class and singleton class behave the same. ST.ancestors includes Foo, so ST.class_variables collects [:@@foo] from Foo.

Ruby 2.7.0 behavior

After Evans' fix, things changed for singleton class. Ruby will collect class variables for ST.class_variables from:

singleton class itself, ST
instance class of singleton class, Bar, see cvar_front_klass below
ancestors of instance class of singleton class, Bar.ancestors

Note that Bar.ancestors doesn't include Foo, so ST.class_variables couldn't find @@foo and returns [].

Take a trip into Evans' code fix

Let's take a deeper look at Evans' fix (section with +):

/* file: variable.c */
  static void*
 mod_cvar_of(VALUE mod, void *data)
 {
     VALUE tmp = mod;
+    if (FL_TEST(mod, FL_SINGLETON)) {
+        if (rb_namespace_p(rb_ivar_get(mod, id__attached__))) {
+            data = mod_cvar_at(tmp, data);
+            tmp = cvar_front_klass(tmp);
+        }
+    }
     for (;;) {
        data = mod_cvar_at(tmp, data);
        tmp = RCLASS_SUPER(tmp);
        if (!tmp) break;
     }
     return data;
 }

The if section was added to use cvar_front_klass of singleton class for later class variables lookup. Here's the cvar_front_klass:

/* file: variable.c */
static VALUE
cvar_front_klass(VALUE klass)
{
    if (FL_TEST(klass, FL_SINGLETON)) {
        VALUE obj = rb_ivar_get(klass, id__attached__);
        if (rb_namespace_p(obj)) {
            return obj;
        }
    }
    return RCLASS_SUPER(klass);
}

From the code we can see:

If klass is singleton class, cvar_front_klass would return the attached object of the singleton class.
For normal class, it just returns ancestor class.

Remember these two behaviors. Below is how Ruby attach object to singleton clss:

/* file: class.c */
/*!
 * Attach a object to a singleton class.
 * @pre \a klass is the singleton class of \a obj.
 */
void
rb_singleton_class_attached(VALUE klass, VALUE obj)
{
    if (FL_TEST(klass, FL_SINGLETON)) {
        if (!RCLASS_IV_TBL(klass)) {
            RCLASS_IV_TBL(klass) = st_init_numtable();
        }
        rb_class_ivar_set(klass, id_attached, obj);
    }
}

From the code we can know that the attached object of a singleton class is actually a class itself. According to this, cvar_front_klass for Bar.singleton_class is Bar. That's why ST.class_variables in Ruby 2.7.0 collects class variables from Bar.ancestors not ST.ancestors

How class_variable_get method works

Let ST = Bar.singleton_class for convenience.

Class variable lookup workflow

Lookup steps for class_variable_get:

Look up on receiver itself. Go to next step if not found.
Look up on cvar_front_klass. Front class for Bar is Bar itself. Front class for ST is the object attached to singleton class, which is also Bar.
Look up in ancestors of cvar_front_klass, which is Bar.ancestors.

From step 2, we can know that:

In our case ST.class_variable_get(:@@foo) is actually equal to Bar.class_variable_get(:@@foo).
And ST.singleton_class.class_variable_get(:@@foo) would look up @@foo on ST and ST's ancestors

Take a trip into class_variable_get method

Let's find out what's inside class_variable_get:

/* file: variable.c */
VALUE
rb_cvar_get(VALUE klass, ID id)
{
    VALUE tmp, front = 0, target = 0;
    st_data_t value;

    tmp = klass;
    CVAR_LOOKUP(&value, {if (!front) front = klass; target = klass;});
    if (!target) {
        rb_name_err_raise("uninitialized class variable %1$s in %2$s",
                          tmp, ID2SYM(id));
    }
    cvar_overtaken(front, target, id);
    return (VALUE)value;
}

The core is CVAR_LOOKUP, which is defined as:

/* file: variable.c */
#define CVAR_LOOKUP(v,r) do {\
    if (cvar_lookup_at(klass, id, (v))) {r;}\
    CVAR_FOREACH_ANCESTORS(klass, v, r);\
} while(0)

It first look up at klass itself, and then in each ancestor of klass. The cvar_lookup_at is a method to find class variable from klass's instance variables table. Think it as a black box with output of a class variable or 0. Right now it's not important in our short trip. Let's see what's inCVAR_FOREACH_ANCESTORS:

/* file: variable.c */
#define CVAR_FOREACH_ANCESTORS(klass, v, r) \
    for (klass = cvar_front_klass(klass); klass; klass = RCLASS_SUPER(klass)) { \
        if (cvar_lookup_at(klass, id, (v))) { \
            r; \
        } \
    }

Got cvar_front_klass again! So if klass here is a singleton class, the for loop would start with instance class of the singleton class, and then iterate through the ancestors of the instance class. That means, when ST.class_variable_get(:@@foo) reaches here, it actually finds @@foo in Bar and Bar.ancestors.

How ST.singleton_class.class_variable_get(:@@foo) works

Let ST = Bar.singleton_class for convenience.

Lookup steps for `ST.class_variable_get(:@@foo)`

@@foo is not found on ST, then it goes to its front class Bar.
Bar doesn't define @@foo. Go to Bar.ancestors.
Oops! Bar.ancestors doesn't contains Foo module, so we can never found @@foo!
Nothing found. End of story.

Lookup steps for `ST.singleton_class.class_variable_get(:@@foo)`

@@foo is not found on ST.singleton_class, then it goes to its front class ST.
ST doesn't define @@foo. Go to ST.ancestors.
@@foo is found on Foo, one of ST.ancestors.
Cool! Let's show 'foo', the value of @@foo!

Final Words

The key to the mystery of original issue is the collecting and lookup workflows of class variables. Mystery is no mystery once you know how it happens.

At last, the following code works at Ruby 2.7.0:

Bar.singleton_class.class_variables
# => []  # <= This is what fixed since 2.7.0

Bar.singleton_class.singleton_class.class_variable_get(:@foo)
# => "foo"  # <= This does not change.

小尾巴

目前待业求职，欢迎介绍远程中高级开发岗位，不胜感激

有远程 Ruby 岗位招人不

zhengpd — Sat, 01 Feb 2020 10:26:54 +0800

新年好！打算看看有没有合适的远程工作岗位。五年 Ruby on Rails 开发经验。

bash-bgnotify: shell command 执行完后自动发出通知

zhengpd — Fri, 22 Apr 2016 22:04:51 +0800

Zsh 插件有个很实用的插件叫 bgnotify ，可以在执行完一个耗时较长的命令后自动发出通知。Bash 不能直接用这个，网上搜了下也没找到类似的插件，于是自己动手把 Zsh 的 bgnotify fork 过来做了些修改用在 Bash 上。因为 Bash 本身并没有 preexec 和 precmd ，所以需要依赖 Bash-Preexec 提供这两个 hook functions。

源码请戳 bash-bgnotify

写了个管理本地 repo 的小工具

zhengpd — Sat, 09 Apr 2016 21:35:56 +0800

写了个管理本地 repo 的小工具，适用场景：

快速 clone 一个感兴趣的 repo 到本地
快速打开本地项目的源码
直接访问本地项目的 README 文件

源码在 https://github.com/zhengpd/vl

写了个 Ruby China 忽略话题的油猴脚本

zhengpd — Sat, 27 Feb 2016 17:05:55 +0800

实现方法是用 localStorage 结合 display: none 隐藏忽略过的话题

https://github.com/zhengpd/userscripts/blob/master/ruby-china-ignore-topics.user.js

列表页：

详情页：

zhengpd (Zheng Piaodan)

启用 chrome custom doh 打不开 ruby china

tmux + nvim 的 pane/window 快速切换

tmux + nvim 的 pane/window 快速切换

缘由

配置

Credits

【建议】关于删除最后回复后的贴子列表排序

Demystify Ruby Class Variables Lookup

发帖前言

Demystify Ruby Class Variables Lookup

Preface

Issue Description

Details Investigation

Related issue report and code fix

How extend method works

How class_variables method works

Ruby 2.6.5 behavior

Ruby 2.7.0 behavior

Take a trip into Evans' code fix

How class_variable_get method works

Class variable lookup workflow

Take a trip into class_variable_get method

How ST.singleton_class.class_variable_get(:@@foo) works

Lookup steps for ST.class_variable_get(:@@foo)

Lookup steps for ST.singleton_class.class_variable_get(:@@foo)

Final Words

小尾巴

有远程 Ruby 岗位招人不

bash-bgnotify: shell command 执行完后自动发出通知

写了个管理本地 repo 的小工具

写了个 Ruby China 忽略话题的油猴脚本

Lookup steps for `ST.class_variable_get(:@@foo)`

Lookup steps for `ST.singleton_class.class_variable_get(:@@foo)`