小编Sam*_*ies的帖子

我想我理解在Clojure交易中通勤和改变的想法之间的基本区别.

更改基本上从事务的开始到结束"锁定"身份,以便多个事务必须按顺序执行.

Commute仅将锁应用于身份的实际值更改,以便事务中的其他操作可以在不同的时间运行,并具有不同的世界视图.

但我对某些事感到困惑.让我们定义一个带有副作用的函数和一个参与的函数:

(defn fn-with-side-effects [state]
    (println "Hello!")
    (inc state))

(def test-counter (ref 0))

现在,如果我们使用alter,我们会看到预期的行为:

user=> (dosync (alter test-counter fn-with-side-effects))
Hello!
1

但是如果我们使用通勤:

user=> (dosync (ref-set test-counter 0))
0
user=> (dosync (commute test-counter fn-with-side-effects))
Hello!
Hello! ; hello is printed twice!
1

因此在通勤版本中,该函数显然仅修改ref一次,因为最终值为1.但是修改器函数的副作用执行两次.为什么会这样？

我几天前升级到El Capitan并跑了一个

brew update && brew upgrade

它更新了imagemagick,导致ruby的rmagick gem停止工作.

没问题,我想,我会跑

gem install rmagick

它会重新编译.

除了它没有,当我运行它时,我看到:

gem install rmagick
Building native extensions.  This could take a while...
ERROR:  Error installing rmagick:
    ERROR: Failed to build gem native extension.

    /Users/sam/.rbenv/versions/2.2.3/bin/ruby -r ./siteconf20151019-57347-30ju1w.rb extconf.rb
checking for clang... yes
checking for Magick-config... yes
checking for outdated ImageMagick version (<= 6.4.9)... no
checking for Ruby version >= 1.8.5... yes
checking for stdint.h... *** extconf.rb failed ***
Could not create Makefile due to some reason, probably …

调试测试可以完美工作，但最近某个时候发生了一些变化，现在却没有（也许是 go 版本升级？）。

当我单击“调试测试”时，会弹出此错误消息：

错误是：Failed to launch: invalid debug configuration - cannot unmarshal bool into "env" of type string

我的launch.json看起来不错（同样，这曾经完美地工作过）：

{
"version": "0.2.0",
"configurations": [
    {
        "name": "Launch test function",
        "type": "go",
        "request": "launch",
        "mode": "test",
        "program": "${workspaceFolder}",
        "env": {
            "LOG_LEVEL": "debug",
            "LOG_SQL": "false",
            "DATABASE_URL": "postgresql://postgres@localhost:5432/chainlink_test?sslmode=disable",
        },
        "args": ["-v"]
    },
]

}

可能出什么问题了？

我无法在Google或stackoverflow上的任何其他位置找到此确切错误.

我正在运行Rails 4.1.0和rspec-rails 3.0.0.beta2

尝试运行$ rspec时,出现以下错误:

    DEPRECATION WARNING: Passing a string to ActiveRecord::Base.establish_connection for a configuration lookup is deprecated, please pass a symbol (:development) instead. (called from <top (required)> at /Users/sam/code/rails/innovacert/spec/spec_helper.rb:4)
/Users/sam/.rvm/gems/ruby-2.1.1/gems/activerecord-4.1.0/lib/active_record/connection_adapters/connection_specification.rb:257:in `resolve_symbol_connection': 'development' database is not configured. Available: ["test"] (ActiveRecord::AdapterNotSpecified)
    from /Users/sam/.rvm/gems/ruby-2.1.1/gems/activerecord-4.1.0/lib/active_record/connection_adapters/connection_specification.rb:240:in `resolve_string_connection'
    from /Users/sam/.rvm/gems/ruby-2.1.1/gems/activerecord-4.1.0/lib/active_record/connection_adapters/connection_specification.rb:267:in `resolve_hash_connection'
    from /Users/sam/.rvm/gems/ruby-2.1.1/gems/activerecord-4.1.0/lib/active_record/connection_adapters/connection_specification.rb:228:in `resolve_connection'
    from /Users/sam/.rvm/gems/ruby-2.1.1/gems/activerecord-4.1.0/lib/active_record/connection_adapters/connection_specification.rb:152:in `resolve'
    from /Users/sam/.rvm/gems/ruby-2.1.1/gems/activerecord-4.1.0/lib/active_record/connection_adapters/connection_specification.rb:164:in `block in resolve_all'
    from /Users/sam/.rvm/gems/ruby-2.1.1/gems/activerecord-4.1.0/lib/active_record/connection_adapters/connection_specification.rb:163:in `each'
    from /Users/sam/.rvm/gems/ruby-2.1.1/gems/activerecord-4.1.0/lib/active_record/connection_adapters/connection_specification.rb:163:in `resolve_all'
    from /Users/sam/.rvm/gems/ruby-2.1.1/gems/activerecord-4.1.0/lib/active_record/connection_handling.rb:69:in `resolve'
    from /Users/sam/.rvm/gems/ruby-2.1.1/gems/activerecord-4.1.0/lib/active_record/core.rb:46:in `configurations='
    from /Users/sam/.rvm/gems/ruby-2.1.1/gems/activerecord-4.1.0/lib/active_record/core.rb:48:in `block in <module:Core>'
    from /Users/sam/.rvm/gems/ruby-2.1.1/gems/activesupport-4.1.0/lib/active_support/concern.rb:120:in `class_eval'
    from /Users/sam/.rvm/gems/ruby-2.1.1/gems/activesupport-4.1.0/lib/active_support/concern.rb:120:in …

我正在尝试运用K&R的2.1.练习内容如下:

写一个程序,以确定的范围char,short,int,和long变量,都signed和unsigned通过打印从标准头合适的值,并通过直接计算.如果计算它们会更难:确定各种浮点类型的范围.

打印标准标题中常量的值很简单,就像这样(例如只显示整数):

printf("Integral Ranges (from constants)\n");
printf("int max: %d\n", INT_MAX);
printf("int min: %d\n", INT_MIN);
printf("unsigned int max: %u\n", UINT_MAX);

但是,我想以编程方式确定限制.

我尝试了这个代码似乎应该可以工作,但它实际上进入一个无限循环并被卡在那里:

printf("Integral Ranges (determined programmatically)\n");

int i_max = 0;

while ((i_max + 1) > i_max) {
        ++i_max;
}

printf("int max: %d\n", i_max);

为什么这会陷入循环？似乎当整数溢出时,它会从2147483647跳转到-2147483648.递增的值显然小于先前的值,因此循环应该结束,但它不会.

我有模板代码,如下所示:

<%= form_for @changeset, @action, fn f -> %>
  <%= if Enum.any?(f.errors) do %>
    <%= for {attr, message} <- f.errors do %>
      <li><%= humanize(attr) %> <%= message %></li>
    <% end %>
  <% end %>
<% end %>

但即使更改集包含错误,也不会打印错误.这是检查的表单结构.请注意,即使错误列表是根据更改集生成的,但错误列表仍为空.

%Phoenix.HTML.Form{data: %BlogPhoenix.Comment{__meta__: #Ecto.Schema.Metadata<:built, "comments">,
  content: nil, id: nil, inserted_at: nil, name: nil, post_id: nil,
  posts: #Ecto.Association.NotLoaded<association :posts is not loaded>,
  updated_at: nil}, errors: [], hidden: [], id: "comment",
 impl: Phoenix.HTML.FormData.Ecto.Changeset, index: nil, name: "comment",
 options: [method: "post"],
 params: %{"content" => nil, "name" …