Multiple dispatch (Re: [squeak-dev] The Inbox: Kernel-cmm.464.mcz)
frank.shearar at angband.za.org
Sun Jun 20 18:35:52 UTC 2010
On 2010/06/20 16:38, Michael Haupt wrote:
> On Sun, Jun 20, 2010 at 4:11 PM, Frank Shearar
> <frank.shearar at angband.za.org> wrote:
>>> Since Smalltalk does not support multi-methods, it is essential that the
>>> caller of a method can pass arguments in multiple formats to the same
>>> method and have them correctly interpreted by the implementation.
>> (I assume you are talking about multiple dispatch - method lookup using not
>> just the receiver but also the types of the parameters to a selector, like
>> Common Lisp's generic functions?)
> looks more like varargs to me ...
I think you're right, Michael.
Objective-C's varargs look like this:
NSString *s = [NSString stringWithFormat: @"a string %@, a float:
%1.2f", @"string", 3.1415];
Note the comma separated values there, in contrast to the more usual
keyword syntax like Smalltalk:
[myObj aSelector: @"hello" withMultiple: 1 args: 2];
The varargs function exactly like &rest parameters in Common Lisp - a
list of values. So it sounds like Brent and Chris want those format
strings (or other vararg-using selectors) to behave the same way with a
single object as with a collection, where the single object is treated
as a single-element collection.
On the implementation side of such a "varargs" method, you'd have
^ (aCollectionOrObject asArray) inject: 0 into: [:total :n | total
:= total + n].
instead of the rather uglier
| coll |
coll := aCollectionOrObject isCollection
ifFalse: [Array with: aCollectionOrObject].
^ (coll asArray) inject: 0 into: [:total :n | total := total + n].
In a library that has many vararg-like selectors, this can make a nice
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