方法ruby中散列的未定义局部变量

for some reason I'm getting

出于某种原因，我得到了

NameError: undefined local variable or method `states' for main:Object

though states is clearly defined. What is going on here?

虽然国家是明确定义的。这里发生了什么？

In irb I added states in and accessed it fine using states[:CA] but when I put it in a method I got that error.

在irb中我添加了状态并使用状态[：CA]访问它，但是当我把它放在一个方法中时我得到了那个错误。

states = {
  CA: 'California',
  FL: 'Florida',
  MI: 'Michigan',
  NY: 'New York',
  OR: 'Oregon',
}

states[:CO] = 'Colorado'
states[:HI] = 'Hawaii'

cities = {
  CA: ['Alameda', 'Apple Valley', 'Exeter'],
  FL: ['Exeter', 'Amelia Island', 'Bunnell'],
  MI: ['Ann Arbor', 'East China', 'Elberta'],
  NY: ['Angelica', 'Apalachin', 'Canadice'],
  OR: ['Amity', 'Boring', 'Camas Valley'],
  CO: ['Blanca', 'Crestone', 'Dillon', 'Fairplay'],
  HI: ['Kailua', 'Hoopili', 'Honolulu'],
}

def describe_state state
  puts state
  description = "#{state.to_s} is for #{states[state]}."
  description << " It has #{citites[state].length} major cities:"
  cities[state].each do |x| ' ' << description end
end

puts describe_state :CA

3 个解决方案

#1

states is a local variable (because it starts with a lowercase letter). Local variables are local to the scope they are defined in (that's why they are called local variables, after all). So, states is defined in the scope of the script, but not in the scope of the method describe_state.

states是一个局部变量（因为它以小写字母开头）。局部变量是它们定义的范围的本地变量（这就是为什么它们被称为局部变量，毕竟）。因此，状态在脚本的范围内定义，但不在describe_state方法的范围内。

Method scopes don't nest, the only scopes that do nest are block scopes, so you would need to use a block. Thankfully, there is a method called define_method which creates a method from a block:

方法范围不嵌套，唯一嵌套的范围是块范围，因此您需要使用块。值得庆幸的是，有一个名为define_method的方法，它从块创建一个方法：

states = {
  CA: 'California',
  FL: 'Florida',
  MI: 'Michigan',
  NY: 'New York',
  OR: 'Oregon',
}

states[:CO] = 'Colorado'
states[:HI] = 'Hawaii'

cities = {
  CA: ['Alameda', 'Apple Valley', 'Exeter'],
  FL: ['Exeter', 'Amelia Island', 'Bunnell'],
  MI: ['Ann Arbor', 'East China', 'Elberta'],
  NY: ['Angelica', 'Apalachin', 'Canadice'],
  OR: ['Amity', 'Boring', 'Camas Valley'],
  CO: ['Blanca', 'Crestone', 'Dillon', 'Fairplay'],
  HI: ['Kailua', 'Hoopili', 'Honolulu'],
}

define_method(:describe_state) do |state|
  "#{state} is for #{states[state]}. " \
  "It has #{cities[state].length} major cities: #{cities[state].join(', ')}"
end

puts describe_state :CA
#=> CA is for California. It has 3 major cities: Alameda, Apple Valley, Exeter

#2

The method can't access the outside variables. You could use instance variables instead. From the documentation:

该方法无法访问外部变量。您可以使用实例变量。从文档：

Instance variables are shared across all methods for the same object.

实例变量在同一对象的所有方法*享。

Example:

例：

@states = {
  CA: 'California',
  FL: 'Florida',
  MI: 'Michigan',
  NY: 'New York',
  OR: 'Oregon',
}

@states[:CO] = 'Colorado'
@states[:HI] = 'Hawaii'

@cities = {
  CA: ['Alameda', 'Apple Valley', 'Exeter'],
  FL: ['Exeter', 'Amelia Island', 'Bunnell'],
  MI: ['Ann Arbor', 'East China', 'Elberta'],
  NY: ['Angelica', 'Apalachin', 'Canadice'],
  OR: ['Amity', 'Boring', 'Camas Valley'],
  CO: ['Blanca', 'Crestone', 'Dillon', 'Fairplay'],
  HI: ['Kailua', 'Hoopili', 'Honolulu'],
}

def describe_state state
  description = "#{state.to_s} is for #{@states[state]}."
  description << " It has #{@cities[state].length} major cities: "
  description << @cities[state].join(', ')
end

puts describe_state :CA
#=> CA is for California. It has 3 major cities: Alameda, Apple Valley, Exeter

(I've fixed a minor bug in describe_state)

（我在describe_state中修复了一个小错误）

#3

states and cities are not defined in the function pass them in like

状态和城市没有定义在函数中传递它们之类的

def describe_state state, states, cities
 ..
end
puts describe_state :CA, states, cities

will work

将工作

#1