Variable methods and accessors in Ruby
Posted by Fred Wu
Yeah I am a lame PHP guy who hasn’t gotten too deeply into Ruby yet. ;)
In PHP I often use variable methods, for example:
$foo = new Foo(); $funcname = 'dynamic_method'; $foo->$funcname(); // Same as calling $foo->dynamic_method(); $varname = 'dynamic_accessor'; $foo->$varname = 'some value'; // Same as calling $foo->dynamic_accessor = 'some value';
Now, because Ruby does not prefix $ in front of variables, it is impossible to use variable methods the way we do in PHP.
I am sure for Ruby gurus it’s pretty obvious but for me, I just spent more than 30 minutes searching for an alternative other than evil eval, and I finally found one.
We use the PHP call_user_func and call_user_func_array equivalent in Ruby: send or __send__.
Luckily accessors in Ruby are methods, so we are able to use the send method for both methods and accessors.
For example we can set a variable accessor like this:
foo = Foo.new
funcname = 'dynamic_method'
foo.send "#{funcname}"
# same as calling foo.dynamic_method
varname = 'dynamic_accessor'
foo.send "#{varname}=", 'some value'
# same as calling foo.dynamic_accessor = 'some value'
I wish in future versions of Ruby, we can somehow assign accessor values the way we do in PHP. :)
I’m a lame ruby guy who has a new project that has to work in php. So I’m the opposite of you. Thanks for the helpful post, although call_user_func isn’t exactly like send because it doesn’t get called on an object.
I miss some of the ruby blocks (locally defined functions) already.
If you really wanted the assign accessors on an object for everything, just override method_missing on an object to automatically set a class variable if called with a “something=” method. :)
This is usually a bad idea – don’t go accessing those private object internals!!
If you want to make them public, use attr_accessor…
class Foo
attr_accessor :dynamic_accessor
end
f= Foo.new
f.dynamic_accessor = 'blah'
If you really want to go peeking into those private internals, you can use instance_variable_get or set…
f.instance_variable_set(:some_var, 'some_value')
# same as inside class Foo doing @some_value
Check out the RDOC for Object class (every objects parent): http://www.ruby-doc.org/core/classes/Object.html
# I kind of like 'send' as a method:
funcname = 'dynamic_method'
foo.send(funcname) # no need for quotes here