Hi --
On Tue, 14 Jul 2009, Buzz Hill wrote:
> Marnen Laibow-Koser wrote:
>
>>>
>>> When you are confused about something, it is sometimes hard to distill
>>> all your thoughts down to the essence of the issue and ask the right
>>> question. But I am trying to define a CONSTANT using the result of an
>>> instance method
>>
>> No you're not. The constant you're trying to define is clearly a class
>> property.
>>
>> If you think about it, this is as it should be. The constant is going
>> to have the same value for every instance of the class. In other words:
>>
>> a = PaymentType.new
>> b = PaymentType.new
>>
>> a and b are now separate instances of PaymentType -- but surely you
>> never want a.PAYMENT_TYPES to be different from b.PAYMENT_TYPES ?
>>
>
> The syntax of a.PAYMENT_TYPES won't work. I am not sure if you meant it
> to work or you were just using it for the sake of explanation.
The syntax will work if you've got an instance method called
PAYMENT_TYPES, but if you don't, it will fail -- whether or not you
have a constant called PAYMENT_TYPES.
> But I get your point, which has enhanced my understanding. Things that
> relate to the class in general, things that shouldn't be redefined, like
> Math:PI are controlled only by class methods. So, in the above example,
> if the payment_types were to change dynamically as the program executed,
> I would not use a constant, I would setup getter and setter methods.
I think you're overthinking it. There's no inherent connection between
constants and class methods.
module MyMathModule
PI = 3.14159265358979
end
puts "PI is #{MyMathModule::PI}"
I've created a module and a constant inside that module. The constant
is resolved using the :: operator, and no methods are involved.
If you define an instance method, you can use the class's constants:
class Rainbow
COLORS = %w{ red orange yellow green blue indigo violet }
def show_me_the_colors
puts "My colors are: #{COLORS.join(", ")}"
end
end
r = Rainbow.new
r.show_me_the_colors
=> My colors are: red, orange, yellow, green, blue, indigo, violet
David
--
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