Ruby on Rails 入门之：(16) Ruby中的定义操作、取消定义操作

判断某个表达式或者变量是否意境定义，可以使用define?语言。如果表达式已经定义会返回一个保存表达式类型的字符串，如果表达式没有定义，那么会返回false

#encoding:gbk
class Test
def Play
puts "Play method";
puts defined?"a>3";
end
end

a = Test.new
puts defined?a.Play;
a.Play;

puts defined?a.Show();

上面输出的结果为：

watkins@watkins:~/temp/workspace/ruby$ ruby define.rb
method
Play method
expression
nil
watkins@watkins:~/temp/workspace/ruby$


释放已经定义的表达式或者变量需要使用undef

#encoding:gbk
class Test
def Play
puts "Play method";
puts defined?"a>3";
end
end

a = Test.new
puts defined?a.Play;
a.Play;

puts defined?a.Show();

puts "************************";

undef Play;
puts defined?a.Play;
输出结果为：

watkins@watkins:~/temp/workspace/ruby$ ruby define.rb
method
Play method
expression
nil
************************
define.rb:17: undefined method `Play' for class `Object' (NameError)
watkins@watkins:~/temp/workspace/ruby$