如何使用新的ruby（1.9）哈希语法从关联中创建符号（哈希键）？ [英] How to create symbol (hash key) from association, using new ruby (1.9) hash syntax?

问题描述

对不起，我甚至不知道如何提出这个问题..所以如果你也可以提出这个问题，不胜感激。

Sorry, I'm not even sure how to ask this question.. so if you could suggest around that as well, it would be appreciated.

# A. WORKS, but "stockroom" is hardcoded
render partial: association.to_s.singularize + '',
  locals: {stockroom: new_object}

# B. WORKS, but uses old syntax
render partial: association.to_s.singularize + '',
  locals: {association.to_s.singularize.to_sym => new_object}

# C. does NOT work
render partial: association.to_s.singularize + '',
  locals: {association.to_s.singularize.to_sym: new_object}

# D. does NOT work
ass = association.to_s.singularize.to_sym
logger.debug "--- ass: #{ass.inspect} (#{ass.class})"
  # => --- ass: :stockroom (Symbol)
render partial: association.to_s.singularize + '', locals: {ass: new_object}

不是旧的语​​法是坏事，我只是想知道是否有一种方法可以使用新的语法（甚至通过中介（即屁股））来执行此操作。 / style>

Not that the old syntax is a bad thing, I'm just wondering if there's a way to do this using the new syntax (even via an intermediary (i.e. ass)).

解析方案

JavaScript风格的语法不是真正的 new 语法，它只是一个在1.9中

You can't use the trailing-colon style with all symbols, try these and you'll see:

{ :$set => 11 }                       # Valid
{ $set: 11 }                          # Invalid
{ :'where.is.pancakes.house?' => 23 } # Valid
{ 'where.is.pancakes.house?': 23 }    # Invalid

同样，如果你有一个符号不是一个符号文字：

Similarly, if you have a symbol that isn't a symbol literal:

s = o.to_sym; { s => 42 }
{ o.to_sym => 42 }

然后你必须在你的Hashes中使用胖箭头语法。如果您有一个不是符号的钥匙，情况也是如此：

then you have to use the fat arrow syntax in your Hashes. The same applies if you have a key that isn't a symbol:

a = %w{where is pancakes house?}
h = { a => 11 }
g = { a: 11 } # Also works but produces a completely different result!

综上所述，尾部分号转换了一些字面值（我认为任何符合 / \A [a-z_] \ w * \ z / i 但我不确定）哈希文字。基本上，除了最琐碎的情况之外，JavaScript风格都是无用的;但微不足道的情况确实是最常见的。

In summary, the trailing-colon converts some literal values (I think anything that matches /\A[a-z_]\w*\z/i but I'm not certain) that precede it to symbols when used inside a Hash literal. Basically, the JavaScript style is useless in all but the most trivial cases; but the trivial cases do happen to be the most common.

我认为使用带有非文字符号的JavaScript风格的唯一方法是像这：

The only way I can think of to use the JavaScript style with a non-literal symbol would be an abomination like this:

ass = association.to_s.singularize.to_sym
h   = eval "{ #{ass}: 'pancakes' }"

如果你曾经在真实代码中加入类似的东西，那么上帝可能会怜悯你的灵魂。

and if you ever put something like that in real code then may the gods have mercy on your soul.

另外，请记住，当你想访问你的哈希时，你必须使用符号的前导符号形式：

Also, keep in mind that you have to use the leading-colon form of the symbol when you want to access your hash:

h[:pancakes] # Valid
h[pancakes:] # Invalid

所以JavaScript样式的效用是有限的。

so the JavaScript style is of limited utility.

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