2、安装完ruby后会提示：Ruby was built without documentation, to build it run: rvm docs generate-ri，所以执行rvm docs generate-ri就可以安装相关文档，ri 类名/模块名/方法名，就可以看到类/模块/方法的文档
有一个叫methods()的方法，比如Array.methods()--------------------------------------------------------- Object#methods
obj.methods=>array
------------------------------------------------------------------------
Returns a list of the names of methods publicly accessible in
_obj_. This will include all the methods accessible in _obj_'s
ancestors.
class Klass
def kMethod()
end
end
k = Klass.new
k.methods[0..9]#=>["kMethod", "freeze", "nil?", "is_a?",
"class", "instance_variable_set",
"methods", "extend", "<em>send</em>", "instance
_eval"]
k.methods.length #=>42
