On 06/20/2012 08:06 PM, Hadley Wickham wrote:
from ?groupGeneric under 'Ops' (of which "+" is one)
used. If different methods are found, there is a warning
about 'incompatible methods': in that case or if no method is
found for either argument the internal method is used.
which doesn't really explain why it works at the command line but not in a
package. S4 methods can be defined on both arguments, so
But aren't the methods compatible? If equality doesn't make a method
compatible what does?
Actually I guess that turns out to be the key (to why they work at the
command line but not in a package). At the command line they really
_are_ the same, e.g., .Internal(inspect("+.a")) has the same address as
"+.b". In the package they (e.g., badadd:::"+.a") have different
addresses, I suppose because S3method() acts on them independently.
setClass("A", contains="numeric")
setClass("B", contains="numeric")
setMethod("+", c("A", "A"), function(e1, e2) message("A + A"))
setMethod("+", c("A", "B"), function(e1, e2) message("A + B"))
setMethod("+", c("B", "A"), function(e1, e2) message("B + A"))
setMethod("+", c("B", "B"), function(e1, e2) message("B + B"))
with
exportClasses("A", "B")
exportMethods("+")
and then
new("A") + new("B")
A + B
NULL
But unfortunately that doesn't work for S3 classes (even with
setOldClass) so it doesn't help much unless we want to rewrite
everything in S4 :/
rewrite?
Hadley
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