Metaprograming question about initialize

Ruby
1

How many times have we seen this:

class X
attr_accessor :arg1, :arg2, :arg3, :arg4

def initialize(arg1, arg2, arg3, arg4)
@arg1, @arg2, @arg3, @arg4 = arg1, arg2, arg3, arg4
end
end

Wouldn’t it be nice if we (ok, I) could instead write

def initialize(arg1, arg2, arg3, arg4)
initargs
end

and have initargs create the attr_accessor as well as the assignments.

I know I can do this in 1.9.2

class X
def initialize(arg1)
self.class.send(:attr_accessor, :arg1)
@arg1 = arg1
end
end

So is it possible in Ruby to introspect on the names of arguments
passed in to a function so that I can build the attr_accessor as well as
the assignments?

2

You can use the Struct class, which implements exactly this.

– Matma R.

3

Monday, February 20, 2012, 3:39:57 AM, you wrote:

BD> You can use the Struct class, which implements exactly this.

BD> – Matma R.

Bartosz,

What I want to do is not change the interface but the implementation.
That is, I want to get a list of the names of the arguments by
introspection.

Ralph

4

2012/2/20 Ralph S. [email protected]:

What I want to do is not change the interface but the implementation. That is,
I want to get a list of the names of the arguments by introspection.

It is much simpler and IMO makes much more sense not to figure out
variable names while already having variables, but to figure out their
contents while having names. Like this:

class Class
def attr_accessor_init *meths
attr_accessor *meths
define_method :initialize do |*args|
meths.each_with_index do |m, i|
self.send :“#{m}=”, args[i]
end
end
end
end

irb(main):013:0> class A
irb(main):014:1> attr_accessor_init :a, :b, :c
irb(main):015:1> end

irb(main):029:0> A.new 4, 6, 8
=> #<A:0xd6cb18 @a=4, @b=6, @c=8>

(This is, essentially, what Struct class does.)

– Matma R.

5

Bartosz,

Monday, February 20, 2012, 10:19:41 AM, you wrote:

BD> 2012/2/20 Ralph S. [email protected]:

What I want to do is not change the interface but the implementation. That is,
I want to get a list of the names of the arguments by introspection.

BD> It is much simpler and IMO makes much more sense not to figure out
BD> variable names while already having variables, but to figure out
their
BD> contents while having names. Like this:

BD> class Class
BD> def attr_accessor_init *meths
BD> attr_accessor *meths
BD> define_method :initialize do |*args|
BD> meths.each_with_index do |m, i|
BD> self.send :“#{m}=”, args[i]
BD> end
BD> end
BD> end
BD> end

irb(main):013:0>> class A
irb(main):014:1>> attr_accessor_init :a, :b, :c
irb(main):015:1>> end

irb(main):029:0>> A.new 4, 6, 8
=>> #<A:0xd6cb18 @a=4, @b=6, @c=8>

BD> (This is, essentially, what Struct class does.)

BD> – Matma R.

This is an elegant solution.

Not quite what I wanted … but I learned a lot from it.

Thank you.

6

Perhaps you are looking for “Kernel#local_variables”.