实例变量,类变量以及它们在ruby中的区别

Question

我很难理解实例变量,类变量以及它们之间在ruby中的区别......有人可以向我解释它们吗？我已经完成了大量的谷歌搜索,完全无法理解它们.

谢谢!

Answer 1

假设您定义了一个类.一个类可以有零个或多个实例.

class Post
end

p1 = Post.new
p2 = Post.new

实例变量在特定实例中作用域.这意味着如果你有一个实例变量title,每个帖子都有自己的标题.

class Post
  def initialize(title)
    @title = title
  end

  def title
    @title
  end
end

p1 = Post.new("First post")
p2 = Post.new("Second post")

p1.title
# => "First post"
p2.title
# => "Second post"

相反,类变量在该类的所有实例之间共享.

class Post
  @@blog = "The blog"

  def initialize(title)
    @title = title
  end

  def title
    @title
  end

  def blog
    @@blog
  end

  def blog=(value)
    @@blog = value
  end
end

p1 = Post.new("First post")
p2 = Post.new("Second post")

p1.title
# => "First post"
p2.title
# => "Second post"

p1.blog
# => "The blog"
p2.blog
# => "The blog"

p1.blog = "New blog"

p1.blog
# => "New blog"
p2.blog
# => "New blog"