Ruby 注入初始值是一个哈希值
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/9434162/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Ruby inject with initial being a hash
提问by Candide
Can any one tell me why the following:
任何人都可以告诉我为什么会出现以下情况：
['a', 'b'].inject({}) {|m,e| m[e] = e }
throws the error:
抛出错误：
IndexError: string not matched
from (irb):11:in `[]='
from (irb):11:in `block in irb_binding'
from (irb):11:in `each'
from (irb):11:in `inject'
from (irb):11
from C:/Ruby192/bin/irb:12:in `<main>'
whereas the following works?
而以下工作？
a = {}
a["str"] = "str"
回答by Rob Davis
Your block needs to return the accumulating hash:
您的区块需要返回累积的哈希值：
['a', 'b'].inject({}) {|m,e| m[e] = e; m }
Instead, it's returning the string 'a' after the first pass, which becomes min the next pass and you end up calling the string's []=method.
相反，它在第一次传递后返回字符串 'a'，它m在下一次传递中变为并且您最终调用字符串的[]=方法。
回答by tokland
The block must return the accumulator (the hash), as @Rob said. Some alternatives:
正如@Rob 所说，该块必须返回累加器（哈希）。一些替代方案：
With Hash#update:
与Hash#update：
hash = ['a', 'b'].inject({}) { |m, e| m.update(e => e) }
With Enumerable#each_with_object:
与Enumerable#each_with_object：
hash = ['a', 'b'].each_with_object({}) { |e, m| m[e] = e }
With Hash#[]:
与Hash#[]：
hash = Hash[['a', 'b'].map { |e| [e, e] }]
With Array#to_h(Ruby >= 2.1):
使用Array#to_h（红宝石 >= 2.1）：
hash = ['a', 'b'].map { |e| [e, e] }.to_h
With Enumerable#mashfrom Facets:
使用来自 Facets 的Enumerable#mash：
require 'facets'
hash = ['a', 'b'].mash { |e| [e, e] }
回答by the Tin Man
Rather than using inject, you should look into Enumerable#each_with_object.
您应该查看Enumerable#each_with_object.
Where injectrequires you to return the object being accumulated into, each_with_objectdoes it automatically.
哪里inject需要你返回被累积的对象，each_with_object它会自动执行。
From the docs:
从文档：
Iterates the given block for each element with an arbitrary object given, and returns the initially given object.
If no block is given, returns an enumerator.
e.g.:
使用给定的任意对象迭代每个元素的给定块，并返回最初给定的对象。
如果没有给出块，则返回一个枚举器。
例如：
evens = (1..10).each_with_object([]) {|i, a| a << i*2 }
#=> [2, 4, 6, 8, 10, 12, 14, 16, 18, 20]
So, closer to your question:
所以，更接近你的问题：
[1] pry(main)> %w[a b].each_with_object({}) { |e,m| m[e] = e }
=> {"a"=>"a", "b"=>"b"}
Notice that injectand each_with_objectreverse the order of the yielded parameters.
请注意，inject并each_with_object反转产生参数的顺序。
