`：key =>是否有区别？ "值"&key：" value"哈希符号？ [英] Is there any difference between the `:key => "value"` and `key: "value"` hash notations?

问题描述

：key =>之间是否有区别？ value（hashrocket）和 key：value（Ruby 1.9）符号？

如果不是，那么我想用键：value表示法。是否有帮助我从：x => 转换为 x：符号的gem？

解决方案

是的，存在差异。这些是合法的：

  h = {：$ in => array} 
 h = {：'a.b'=> 'c'} 
h [：s] = 42 
  

但这些不是：

  h = {$ in：array} 
h = {'a.b'：'c'}＃但这是可以在Ruby2.2 + 
h中使用[s：] = 42 
  

作为 =>> 的关键，所以你可以这样做：

  h = {C.new => 11} 
 h = {23 => 'pancakes house？'} 
  

但是您不能这样做：

  h = {C.new：11} 
h = {23：'煎饼屋？'} 
  

JavaScript样式（ key：value ）仅在所有Hash键都是简单符号（或多或少与 / \ A [a-z_] \ w \\ \ z / i 相匹配的东西，AFAIK解析器使用它的标签模式对于这些键）。

使用MongoDB时，：$ in 样式符号显示出合理的位，如果您使用MongoDB，最终会混合哈希样式。而且，如果您曾经使用Hashes的特定键（ h [：k] ）而不是整个哈希（ h = {...} ），您仍然必须使用符号的冒号优先样式;您还必须使用引号分隔样式来表示您在哈希之外使用的符号。我更喜欢保持一致性，所以我根本不打扰JavaScript风格。

在Ruby 2.2中，JavaScript风格的一些问题已得到解决。如果您的符号不是有效标签，您现在可以使用引号，例如：

  h = {'其中是' ：'pancakes house？'，'$ set'：{a：11}} 
  

但你仍然如果你的钥匙不是符号的话，需要使用hashrocket。

Is there any difference between :key => "value" (hashrocket) and key: "value" (Ruby 1.9) notations?

If not, then I would like to use key: "value" notation. Is there a gem that helps me to convert from :x => to x: notations?

解决方案

Yes, there is a difference. These are legal:

h = { :$in => array }
h = { :'a.b' => 'c' }
h[:s] = 42

but these are not:

h = { $in: array }
h = { 'a.b': 'c' } # but this is okay in Ruby2.2+
h[s:] = 42

You can also use anything as a key with => so you can do this:

h = { C.new => 11 }
h = { 23 => 'pancakes house?' }

but you can't do this:

h = { C.new: 11 }
h = { 23: 'pancakes house?' }

The JavaScript style (key: value) is only useful if all of your Hash keys are "simple" symbols (more or less something that matches /\A[a-z_]\w*\z/i, AFAIK the parser uses its label pattern for these keys).

The :$in style symbols show up a fair bit when using MongoDB so you'll end up mixing Hash styles if you use MongoDB. And, if you ever work with specific keys of Hashes (h[:k]) rather than just whole hashes (h = { ... }), you'll still have to use the colon-first style for symbols; you'll also have to use the leading-colon style for symbols that you use outside of Hashes. I prefer to be consistent so I don't bother with the JavaScript style at all.

Some of the problems with the JavaScript-style have been fixed in Ruby 2.2. You can now use quotes if you have symbols that aren't valid labels, for example:

h = { 'where is': 'pancakes house?', '$set': { a: 11 } }

But you still need the hashrocket if your keys are not symbols.

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