Re: switch using strings

Joshua Cranmer <Pidgeot18@verizon.invalid>
Thu, 24 Feb 2011 21:51:41 -0500
On 02/24/2011 03:57 PM, Tom Anderson wrote:

On Wed, 23 Feb 2011, Joshua Cranmer wrote:

or you should have a neater pattern to access the classes. If the
classes are logically related, you probably ought to do a visitor
pattern (e.g., source code ASTs).

That's what i'd usually do. But thinking about it, i don't see why it's
preferable to my hypothetical class switch. What's the benefit? How does
using a visitor rather than a switch help me deliver more value to my

The visitor case is a poor man's implementation of double dispatch (I
meant this earlier when I said "dynamic dispatch"... I suppose 7 PM is
not the time to be rebutting posts...).

In the case of String v. double v. <something>, handling data
internally as a type-tagged system would allow you to use polymorphism
to suit your needs. In the worst case, you could always use a
reflection-based approach to implement true dynamic dispatch (ew,
maybe invokedynamic would neatify that).

That has got to be the fastest abandonment of the technical high ground
i have ever seen. Did you use a sledge? :)

The real answer to a switch-based-on-class, I think, would be double
dispatch. However, Java doesn't really support double dispatch, and I'm
not sure whether or not it should.

It's mostly a contrived example. I mean, we do actually have some logic
almost exactly like that, but we recognise it's a mistake and are
working on getting rid of it!

I'll grant you that it is a contrived example, but one would hope that a
contrived example would be more persuasive in explaining why a feature
would be useful...

How nice of you to include support for the case when two cases go to
the same thing. That is by far my biggest (and I think only?) use of
fall-through in switches.

Duff's device!

Hmm, I should put that on a test and ask people what it does and why it
works. I wonder if the average on that question would be above or below 25%.

Beware of bugs in the above code; I have only proved it correct, not
tried it. -- Donald E. Knuth

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