Trying to understand method calls in a class body. Fundamentally, why doesn't this work?

Ruby
1

My understanding is that method calls in a class body are called as soon
as the ruby interpreter interprets them. Are these not working because
method calls in a class body are executed before the definition of the
instance/class methods?

http://pastie.org/private/u19k8wtwapi6jxzozlcpqq#3,13,24,36

Regards,

Jorge

Senior Software Architect/Owner
2UP Media
c: 407.489.2677
[email protected]
www.2upmedia.com

LinkedIn
PHP Zend Certified Engineer

2

On Dec 5, 2014, at 20:26, Jorge C. [email protected] wrote:

My understanding is that method calls in a class body are called as soon as the
ruby interpreter interprets them. Are these not working because method calls in a
class body are executed before the definition of the instance/class methods?

http://pastie.org/private/u19k8wtwapi6jxzozlcpqq#3,13,24,36
http://pastie.org/private/u19k8wtwapi6jxzozlcpqq#3,13,24,36

You’re defining instance methods, but method calls in a class body
invoke class methods; there’s no instance to invoke instance methods on.

3

On Dec 5, 2014, at 20:34, Jorge C. [email protected] wrote:

Bryce,

Since I’m essentially passing in an instance “dude” to the singleton class, is
the class body still in the context of a class and NOT the instance "dude?

Correct:

[3] pry(main)> puts dude.inspect
#
=> nil
[4] pry(main)> class << dude
[4] pry(main)* puts inspect
[4] pry(main)* end
#<Class:#<#Class:0x007fb0d3ec6568:0x007fb0d3ec64f0>>

4

Ok. That makes sense. Out of pure curiosity, is there any “hacky” way to
call instance methods in a class context?

Regards,

Jorge

Senior Software Architect/Owner
2UP Media
c: 407.489.2677
[email protected]
www.2upmedia.com

LinkedIn
PHP Zend Certified Engineer

5

On Dec 5, 2014, at 20:46, Jorge C. [email protected] wrote:

Ok. That makes sense. Out of pure curiosity, is there any “hacky” way to call
instance methods in a class context?

I cant think of one off the top of my head, but at the same time, I dont
normally see the value in metaprogramming with eigenclasses (thats the
per-object class youre adding methods to). Its tricky to write (as youre
finding out), and its even more tricky to test, fix, and debug later.

6

Bryce,

Since I’m essentially passing in an instance “dude” to the singleton
class, is the class body still in the context of a class and NOT the
instance “dude”?

Regards,

Jorge

Senior Software Architect/Owner
2UP Media
c: 407.489.2677
[email protected]
www.2upmedia.com

LinkedIn
PHP Zend Certified Engineer

7

Thanks for the clarification. It was very much appreciated. Hope you
enjoy your weekend.

Regards,

Jorge

Senior Software Architect/Owner
2UP Media
c: 407.489.2677
[email protected]
www.2upmedia.com

LinkedIn
PHP Zend Certified Engineer

8

On Sat, Dec 6, 2014 at 2:46 AM, Jorge C. [email protected] wrote:

Ok. That makes sense. Out of pure curiosity, is there any “hacky” way to
call instance methods in a class context?

You’d first need an instance. Without creating one or passing an
instance on it won’t work.

Here is a way that does what I assume you want

Struct.new(:name).new(“John D.”).tap do |dude|
class << dude
attr_accessor :is_single
end

dude.send :is_single=, true
end

That code is still quite odd (esp. considering your advertised
position) and I would not recommend doing this. There are much
simpler ways to go about things.

Person = Struct.new :name, :is_single
dude = Dudish.new “John D.”, true

There are other approaches, depending on what you want to achieve:

anonymous class

dude = Struct.new(:name, :is_single).new “John D.”, true

anonymous class, other constructor call

dude = Struct.new(:name, :is_single)[“John D.”, true]

not a regular Struct member

Person = Struct.new(:name) do
attr_accessor :is_single
end

dude = Person.new “John D.”
dude.is_single = true

both

dude = Struct.new(:name) do
attr_accessor :is_single
end.new “John D.”

dude.is_single = true

variant

dude = Struct.new(:name) do
attr_accessor :is_single
end.new(“John D.”).tap |o|
o.is_single = true
end

Cheers

robert