小编bog*_*ogl的帖子

我试图理解这个榆树构造:

type Item = Item { name : String, data : String }

• 它类似于记录,但它的行为却截然不同.
• 它对于定义递归数据模型很有用.
• type alias Item = {...}与之不同,它不提供"构造函数".
• 我在Elm Syntax指南中找不到它.
• 我无法弄清楚如何访问其字段:

> item = Item { name = "abc", data  = "def" } 
Item { name = "abc", data = "def" } : Repl.Item

> item.name
-- TYPE MISMATCH --------------------------------------------- repl-temp-000.elm

`item` does not have a field named `name`.

6|   item.name
     ^^^^^^^^^ The type of `item` is:

    Item

Which does not contain a field named `name`.

• 这个结构如何调用？ …

在调试具有某种复杂性的ruby代码时,很容易被堆叠的方法定义和命名与局部变量的冲突混淆.

我正在寻找一种快速的方法来找出哪个方法或变量响应表达式,例如any_expression.identify.

到目前为止我能找到的最好的是:

method(:happy)
#=> #<Method: Object(Helper)#happy>

method(:happy).source_location
#=> ["/home/somebody/project/lib/helper.rb", 9]

不幸的是,一个局部变量(如happy=42)会先于,但method(:happy)仍将返回另一个方法.

有任何想法吗？

我正在尝试在Ubuntu 15.10（Wily）上安装ruby-qml。显然缺少一些先决条件：

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

    /usr/bin/ruby2.1 extconf.rb
checking for qmake... yes
  >>> building libqmlbind...
Project ERROR: Unknown module(s) in QT: qml quick
make: *** No targets specified and no makefile found.  Stop.
ERROR: Failed to build libqmlbind
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the …