Why a class when there will only be one instance?

[Peter Maas]

SeeBelow at SeeBelow.Nut wrote:
> Even easier is not to make anything a class unless there will be two or
> more instances of it.  I still don't get what advantage making a class
> buys for you.

To use classes even in single instance cases has some advantages:

- There is a unique way of organizing your code.

- There is an easy transition to the multiple instance case.

- It makes writing meta code (e.g. for documentation, transformation
   ...) easier.

- Code organisation should resemble the real world problem to be modeled
   (for the sake of clarity): if emphasis is on an entity (e.g. a document)
   use an object, if emphasis is on activity (e.g. computing the cosine)
   use a function.

These advantages outweigh by far lexical arguments (self. takes soooo long
to type) or temporary arguments (instance count is currently = 1).

Of course this is largely a matter of taste but I am a 'burnt child'
because I had to deal with the one-instance argument in multi-developer
projects and found the defender's code quite messy. :)

> Other people have mentioned "code reuse".  Again I don't see how a class
> helps to make code reusable.

Inheritance.

> I find methods in a class more difficult to reuse than simple function
 > definitions.  (unless there are multiple instances.)

Why? Methods are functions with an instance argument:

class person:
     def tellName(self):
         print self.name

 >>> p = person()
 >>> p.name = 'Peter'
 >>> intro_c = person.tellName
 >>> intro_c(p)
Peter
 >>> intro_i = p.tellName
 >>> intro_i()
Peter

Mit freundlichen Gruessen,

Peter Maas

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