Call a generic function with or without parameters - ruby-on-rails

Question

I had a code looking like this:
def my_function(obj)
if obj.type == 'a'
return [:something]
elsif obj.type == 'b'
return []
elsif obj.type == 'c'
return [obj]
elsif obj.type == 'd'
return [obj]*2
end
end
I want to separate all these if...elsif blocks into functions like this:
def my_function_with_a
return [:something]
end
def my_function_with_b
return []
end
def my_function_with_c(a_parameter)
return [a_parameter]
end
def my_function_with_d(a_parameter)
return [a_parameter] * 2
end
I call these functions with
def my_function(obj)
send(:"my_function_with_#{obj.type}", obj)
end
The problem is that some functions need parameters, others do not. I can easily define def my_function_with_a(nothing=nil), but I'm sure there is a better solution to do this.
#Dogbert had a great idea with arity. I have a solution like this:
def my_function(obj)
my_method = self.method("my_function_with_#{obj.type}")
return (method.arity.zero? ? method.call : method.call(obj))
end

Answer 1

Check how to call methods in Ruby, for that I will recommend you this two resources: wikibooks and enter link description here.
Take a special note on optional arguments where you can define a method like this:
def method(*args)
end
and then you call call it like this:
method
method(arg1)
method(arg1, arg2)

Answer 2

def foo(*args)
[ 'foo' ].push(*args)
end
>> foo
=> [ 'foo' ]
>> foo('bar')
=> [ 'foo', 'bar' ]
>> foo('bar', 'baz')
=> [ 'foo', 'bar', 'baz' ]

Answer 3

def my_function(obj)
method = method("my_function_with_#{obj.type}")
method.call(*[obj].first(method.arity))
end

Answer 4

Change your function to something like:
def my_function_with_foo(bar=nil)
if bar
return ['foo', bar]
else
return ['foo']
end
end
Now the following will both work:
send(:"my_function_with_#{foo_bar}")
=> ['foo']
send(:"my_function_with_#{foo_bar}", "bar")
=> ['foo', 'bar']
You can also write it like this if you don't want to use if/else and you're sure you'll never need nil in the array:
def my_function_with_foo(bar=nil)
return ['foo', bar].compact
end

Answer 5

You can use a default value
def fun(a_param = nil)
if a_param
return ['raboof',a_param]
else
return ['raboof']
end
end
or...
def fun(a_param : nil)
if a_param
return ['raboof',a_param]
else
return ['raboof']
end
end
The latter is useful if you have multiple parameters because now when you call it you can just pass in the ones that matter right now.
fun(a_param:"Hooray")