how to define a method template

[Nanyang Zhan]

Forgive me for the nonstandard words. I will describe my problem in
details:
I am doing a rails app, and met a ruby problem.
Inside a model class, I will need to write these codes for "apple"
def apple_attr
apples.collect {|o| o.name}.join(" ")
end

def apple_attr=(str)
@apple = str
end

def save_apple
#lots of codes
end

then banana, cat, dog.. each will have a copy of above codes. They are
the same, except replacing the word "apple" with "banana", "cat",
"dog"....

I know there is a way to put these code in to a module, then mixin the
module with current class, after that, you just need to call a method
(like setup_methodsapple); setup_methodsdog)...), instead of typing
the repeated code.

Would any one tell me how to do it?

 

[Robert Klemme]

Forgive me for the nonstandard words. I will describe my problem in
details:
I am doing a rails app, and met a ruby problem.
Inside a model class, I will need to write these codes for "apple"
def apple_attr
apples.collect {|o| o.name}.join(" ")
end

def apple_attr=(str)
@apple = str
end

def save_apple
#lots of codes
end

then banana, cat, dog.. each will have a copy of above codes. They are
the same, except replacing the word "apple" with "banana", "cat",
"dog"....

I know there is a way to put these code in to a module, then mixin the
module with current class, after that, you just need to call a method
(like setup_methodsapple); setup_methodsdog)...), instead of typing
the repeated code.

Would any one tell me how to do it?

Why not create all the methods on the fly? Like

class Foo
def setup_methods(sym)
cl = class <<self;self;end
cl.class_eval do
attr_accessor sym
end
cl.class_eval "def #{sym}_save() puts 'saving #{sym}' end"
end
end

Now you can do

irb(main):010:0> f=Foo.new
=> #<Foo:0x7ff74f48>
irb(main):011:0> f.apple
NoMethodError: undefined method `apple' for #<Foo:0x7ff74f48>
from (irb):11
from :0
irb(main):012:0> f.setup_methods :apple
=> nil
irb(main):013:0> f.apple
=> nil
irb(main):014:0> f.apple="foo bar"
=> "foo bar"
irb(main):015:0> f.apple
=> "foo bar"
irb(main):016:0> f.apple_save
saving apple
=> nil
irb(main):017:0>

Kind regards

robert

 

[Robert Klemme]

Why not create all the methods on the fly? Like

class Foo
def setup_methods(sym)
cl = class <<self;self;end
cl.class_eval do
attr_accessor sym
end
cl.class_eval "def #{sym}_save() puts 'saving #{sym}' end"
end
end

Now you can do

irb(main):010:0> f=Foo.new
=> #<Foo:0x7ff74f48>
irb(main):011:0> f.apple
NoMethodError: undefined method `apple' for #<Foo:0x7ff74f48>
from (irb):11
from :0
irb(main):012:0> f.setup_methods :apple
=> nil
irb(main):013:0> f.apple
=> nil
irb(main):014:0> f.apple="foo bar"
=> "foo bar"
irb(main):015:0> f.apple
=> "foo bar"
irb(main):016:0> f.apple_save
saving apple
=> nil
irb(main):017:0>

Kind regards

robert

PS: of course you can define setup_methods in a module and mixin that
module.

 

[Robert Dober]

Why not create all the methods on the fly? Like

class Foo
def setup_methods(sym)
cl = class <<self;self;end
cl.class_eval do
attr_accessor sym
end
cl.class_eval "def #{sym}_save() puts 'saving #{sym}' end"
end
end

Robert I have understood the setup a little bit differently, was it
not on the class base that OP wanted his methods?

Your technique of course is correct, just that - if I were right - OP
needed this

class Foo

%w{ apple banana mango strawberry }.each do
|fruit|
define_method "#{fruit}_attr" do
send(fruit.pluralize).map{|f|f.name}.join(",")
end
define_method "#{fruit}_attr=" do
| str |
instance_variable_set("@" << fruit, str)
end
define_method "save_" << fruit do
# lots of code adapted to metaprogramming, which might be possible
# or not
end
end
end

Now you can do

irb(main):010:0> f=Foo.new
=> #<Foo:0x7ff74f48>
irb(main):011:0> f.apple
NoMethodError: undefined method `apple' for #<Foo:0x7ff74f48>
from (irb):11
from :0
irb(main):012:0> f.setup_methods :apple
=> nil
irb(main):013:0> f.apple
=> nil
irb(main):014:0> f.apple="foo bar"
=> "foo bar"
irb(main):015:0> f.apple
=> "foo bar"
irb(main):016:0> f.apple_save
saving apple
=> nil
irb(main):017:0>

Kind regards

robert

f = Foo.new # has methods like apples_attr, save_strawberry and
banana_attr= already, which might make sense or not

HTH
Robert

 

[Robert Klemme]

Robert I have understood the setup a little bit differently, was it
not on the class base that OP wanted his methods?

Maybe. His statement seems to be a bit contradictory. First he talks
about all these methods being there. Then he mentions some method
setup_methods which I believe is to create those methods. But you're
right, could also be a class method (like attr_accessor). OP, what do
you want - Robert's solution or Robert's solution?

Kind regards

robert

 

[Robert Dober]

Maybe. His statement seems to be a bit contradictory. First he talks
about all these methods being there. Then he mentions some method
setup_methods which I believe is to create those methods. But you're
right, could also be a class method (like attr_accessor). OP, what do
you want - Robert's solution or Robert's solution? Difficult decision LOL

Kind regards

robert

 

[Nanyang Zhan]

OP, what do you want - Robert's solution or Robert's solution?

Kind regards

robert

Thanks RobertS!
Now I'm pretty sure that people tend to using the programming languages
that has the same character with their names, like Roberts will pick up
Ruby while Johns prefer Java.

Robert Dober's solution offer me details on how to write the codes about
defining those methods. It will be very useful, but still I have no idea
where to put these definitions.
Robert's solution(yes, that's Robert Klemme) needs to be adjusted to fit
my requirement correctlly. But it's very interesting. Robert, Can you
tell me how to make setup_methods :apple can be called inside a class,
like:

#magic codes put here, then
Class Fruit < ActiveRecord::Base
# create all the methods on the fly
setup_methods :apple
setup_methods :banana
....
# call methods that are created on the fly inside a class
after_save :save_apple
after_save :save_banana
end

That is, please tell me how to mixin.

 

[Nanyang Zhan]

I just managed to apply Dober's codes into my app (I just copy the code
into the class, and add some codes), It is just that simple, but works
fine! Still, I get a problem, inside

define_method "save_" << fruit do
#HERE
end

this method, I need to call a local method with the same name as string
fruit contains. If it is a instance variable, I know there are
instance_variable_set("@#{fruit}", str) and
instance_variable_get("@#{fruit}") methods. But what about this local
method? How can I read/set its value?

Though the problem inside the class is almost solved, but I still want
to know the mixin solution, because with mixin solution, I can use these
code almong other classes.

 

[Robert Klemme]

Thanks RobertS!
Now I'm pretty sure that people tend to using the programming languages
that has the same character with their names, like Roberts will pick up
Ruby while Johns prefer Java.

Actually I do Java for a living - and I don't hate it.

Robert Dober's solution offer me details on how to write the codes about
defining those methods. It will be very useful, but still I have no idea
where to put these definitions.
Robert's solution(yes, that's Robert Klemme) needs to be adjusted to fit
my requirement correctlly. But it's very interesting. Robert, Can you
tell me how to make setup_methods :apple can be called inside a class,
like:

#magic codes put here, then
Class Fruit < ActiveRecord::Base
# create all the methods on the fly
setup_methods :apple
setup_methods :banana
...
# call methods that are created on the fly inside a class
after_save :save_apple
after_save :save_banana
end

That is, please tell me how to mixin.

Basically you can define a method setup_methods in class Class. Untested:

class Class
def setup_methods(sym)
class_eval do
attr_accessor sym
end
class_eval "def #{sym}_save() puts 'saving #{sym}' end"
end
end

Kind regards

robert

 

[Nanyang Zhan]

Actually I do Java for a living - and I don't hate it.

why hate it? while it makes you living and others happy...

Basically you can define a method setup_methods in class Class.

Then I can call the methods it defines anywhere I like?