Some example code
class MySuperClass
def initialize *args
puts "In SuperClass initialize"
end
end
class MySubClass1 < MySuperClass
def initialize name
puts "In SubClass initialize: " + name
super
end
end
The super in the subclass will take with it any parameters that were
sent to the initialize method, so this will throw an error as the
initialize in MySuperClass does not accept the same number of
parameters.
This is surprisingly restrictive (given the nature of Ruby generally).
If you are extending a class with a parameterless initializer, you
cannot access the superclass initializer if you want to include a
parameter.
The initialize method is automatically private (and appears to be stuck
like that), so cannot be invoked through super.initialize or something
like that.
Three possible workarounds: When you create an initialize method, always
have a parameter with a default value, even if you just discard it. This
will allow subclasses to have zero or one parameters, and effectively
any number through a hash. A better way perhaps is to use *args as the
parameter list, even if you do not use it. If you cannot modify the
superclass (say it is in someone else's API), the nly alternatiove I can
think of is to initialise with another method, say init, but then you
are relying on any API user remembering to do that - the whole point of
initialize is so they (and you) do not have to remember.
These are all hacks. Is there a better way? Or have I missed something?
···
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Hi,
Some example code
class MySuperClass
def initialize *args
puts "In SuperClass initialize"
end
end
class MySubClass1 < MySuperClass
def initialize name
puts "In SubClass initialize: " + name
super
end
end
The super in the subclass will take with it any parameters that were
sent to the initialize method, so this will throw an error as the
initialize in MySuperClass does not accept the same number of
parameters.
This is surprisingly restrictive (given the nature of Ruby generally).
If you are extending a class with a parameterless initializer, you
cannot access the superclass initializer if you want to include a
parameter.
Why not? You can explicitly provide arguments to super, e.g.
super(arg1, arg2)
to call a method of super class. You can call it without any argument
by
super()
note that it's different from "super".
matz.
···
In message "Re: initialize and super with parameters" on Fri, 4 Jul 2008 23:26:46 +0900, Andy Joel <ak_joel@hotmail.com> writes:
You want to use
super()
instead of just
super
It is one of the few situations (if not the only) where adding the parentheses
to a method call changes its behavior. In particular, super without
parentheses calls the method of the base class with all the arguments passed
to the current method; super() instead calls the method of the base class
without arguments.
Stefano
···
On Friday 04 July 2008, Andy Joel wrote:
Some example code
class MySuperClass
def initialize *args
puts "In SuperClass initialize"
end
end
class MySubClass1 < MySuperClass
def initialize name
puts "In SubClass initialize: " + name
super
end
end
The super in the subclass will take with it any parameters that were
sent to the initialize method, so this will throw an error as the
initialize in MySuperClass does not accept the same number of
parameters.
This is surprisingly restrictive (given the nature of Ruby generally).
If you are extending a class with a parameterless initializer, you
cannot access the superclass initializer if you want to include a
parameter.
The initialize method is automatically private (and appears to be stuck
like that), so cannot be invoked through super.initialize or something
like that.
Three possible workarounds: When you create an initialize method, always
have a parameter with a default value, even if you just discard it. This
will allow subclasses to have zero or one parameters, and effectively
any number through a hash. A better way perhaps is to use *args as the
parameter list, even if you do not use it. If you cannot modify the
superclass (say it is in someone else's API), the nly alternatiove I can
think of is to initialise with another method, say init, but then you
are relying on any API user remembering to do that - the whole point of
initialize is so they (and you) do not have to remember.
These are all hacks. Is there a better way? Or have I missed something?
Take a look at FAQ 5.9 here for your answer [1]. The call to "super" is not a real method call. When you call "super" without any params or parentheses, it starts the method lookup for the current method name but starting in the superclass while passing along all parameters (if any). If the superclass' method signature is different, you must explicitly tell super what to pass. If there are no parameters at all, empty parens () are sufficient.
class A
def initialize
puts "superclass"
end
end
class B < A
def initialize(name)
puts "my name is #{name}"
super # <== wrong
end
end
B.new("Chuck")
This will throw an ArgumentError. Change the subclass like so:
class B < A
def initialize(name)
puts "my name is #{name}"
super()
end
end
B.new("Chuck")
All is well with the world.
cr
[1] http://www.math.ias.edu/doc/ruby-docs-1.8.2/faq-en/rubyfaq-5.html
···
On Jul 4, 2008, at 9:26 AM, Andy Joel wrote:
Some example code
class MySuperClass
def initialize *args
puts "In SuperClass initialize"
end
end
class MySubClass1 < MySuperClass
def initialize name
puts "In SubClass initialize: " + name
super
end
end
The super in the subclass will take with it any parameters that were
sent to the initialize method, so this will throw an error as the
initialize in MySuperClass does not accept the same number of
parameters.
This is surprisingly restrictive (given the nature of Ruby generally).
If you are extending a class with a parameterless initializer, you
cannot access the superclass initializer if you want to include a
parameter.
You want to use
super()
instead of just
super
It is one of the few situations (if not the only) where adding the
parentheses
to a method call changes its behavior. In particular, super without
parentheses calls the method of the base class with all the arguments
passed
to the current method; super() instead calls the method of the base class
without arguments.
Stefano
Note that you can also call the inherited initialize with any other
parameters if you like, such as:
super(:cactus, :fridge_magnet, Caribu.new, {:args_in=>some_args_i_got})
So it's pretty felxible, really 
Cheers,
Benjohn
Stefano Crocco wrote:
You want to use
super()
instead of just
super
It is one of the few situations (if not the only) where adding the
parentheses
to a method call changes its behavior. In particular, super without
parentheses calls the method of the base class with all the arguments
passed
to the current method; super() instead calls the method of the base
class
without arguments.
Stefano
Thanks for the prompt replies everyone. So I had just missed something,
which is good news.
···
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