如何动态创建局部变量? [英] How to dynamically create a local variable?

问题描述

我有一个变量 var = "some_name"，我想创建一个新对象并将其分配给 some_name.我该怎么做?例如

I have a variable var = "some_name" and I would like to create a new object and assign it to some_name. How can I do it? E.g.

var = "some_name"
some_name = Struct.new(:name) # I need this
a = some_name.new('blah') # so that I can do this.

推荐答案

您不能在 Ruby 1.9+ 中动态创建局部变量(您可以在 Ruby 1.8 中通过 eval):

You cannot dynamically create local variables in Ruby 1.9+ (you could in Ruby 1.8 via eval):

eval 'foo = "bar"'
foo  # NameError: undefined local variable or method `foo' for main:Object

不过，它们可以在 eval-ed 代码本身中使用:

They can be used within the eval-ed code itself, though:

eval 'foo = "bar"; foo + "baz"'
#=> "barbaz"

Ruby 2.1 添加了 local_variable_set，但这不能创建新的局部变量:

Ruby 2.1 added local_variable_set, but that cannot create new local variables either:

binding.local_variable_set :foo, 'bar'
foo # NameError: undefined local variable or method `foo' for main:Object

这种行为不能在不修改 Ruby 本身的情况下被改变.另一种方法是考虑将您的数据存储在另一个数据结构中，例如一个哈希，而不是许多局部变量:

This behavior cannot be changed without modifying Ruby itself. The alternative is to instead consider storing your data within another data structure, e.g. a Hash, instead of many local variables:

hash = {}
hash[:my_var] = :foo

<小时>

请注意，eval 和 local_variable_set do 都允许重新分配现有的局部变量:

---

Note that both eval and local_variable_set do allow reassigning an existing local variable:

foo = nil
eval 'foo = "bar"'
foo  #=> "bar"
binding.local_variable_set :foo, 'baz'
foo  #=> "baz"

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