On 14 Feb 2006, [EMAIL PROTECTED] wrote:
> It seems to me like the generic should (always?) just have arguments
> used for dispatch -- stream, in this case -- and that methods then
> specify default values.
There are advantages to adding named arguments to a generic to define
the expected interface. These 'extra' args may not be *needed* for
dispatch in the sense that the first arg may be enough to decide what
method you want.
So IMO, there are two reasons to put an arg in a generic:
1. You really want to dispatch on it.
2. You want to define an interface and can handle the fact that you
will have to also dispatch on it.
I guess my point is that for downstream developers extending your
generic and for the sake of documentation, relying too much on '...'
can make things difficult.
> To also dispatch on the second argument, one
> might
>
> setGeneric("rstream.sample",
> function( stream, n, ... ) standardGeneric("rstream.sample"))
>
> setMethod("rstream.sample", c( "rstream.sample", "numeric" ),
> function( stream, n, ... ) { code } )
>
> setMethod("rstream.sample", c( "rstream.sample", "missing" ),
> function( stream, n, ... ) rstream.sample( stream, n = 1 ))
And here I might offer a slight improvement. Putting the default
value in the signature of the function will give automated tools a
chance to document:
setMethod("rstream.sample", c("rstream.sample", "missing"),
function( stream, n=1, ...) rstream.sample(stream, n))
+ seth
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