Attr_read, attr_writer, etc

Ruby
1

Hello,
are these keywords or are they methods which create get/set methods for
the given attribute?

I suppose it’s a mix of both, because I tried to write my own
attr_accessor but I couldn’t call it in the class definition, only on
an existing object.

Turing.

2

Thanks for your explanation, but how would you write a attr_writer
method?
I don’t know how I can pass a parameter list to define_method.

Turing.

3

Alle lunedì 13 agosto 2007, Frank M. ha scritto:

Turing.

They’re instance method of the Module class. You can write them, if you
want:

class Module

def my_attr_reader *args
args.each do |a|
define_method(a) do
puts ‘this method was generated by my_attr_reader’;
instance_variable_get("@#{a}")
end
end
end

end

class C
my_attr_reader :x

def initialize x
@x = x
end
end

res = C.new(2).x
=> this method was generated by my_attr_reader
puts res
=> 2

Defining my_attr_reader in class Module will make it availlable in all
classes
and modules. You can define it in class Class to make it availlable only
in
classes, or you can define them in a single class. In this case,
however, it
should be defined as a class method, not as an instance method:

class MyClass
def self.my_attr_reader
…

I hope this helps

Stefano

4

Hi –

On Tue, 14 Aug 2007, Frank M. wrote:

Thanks for your explanation, but how would you write a attr_writer
method?
I don’t know how I can pass a parameter list to define_method.

Give the block a parameter:

def my_attr_writer(*names)
names.each do |name|
define_method("#{name}=") {|x| instance_variable_set("@#{name}",
x) }
end
end

David