On 11/02/2011 06:52 AM, Albert-Jan Roskam wrote:
Hello,
I would like to overload the + operator so that it can be used to concatenate two strings, e.g
John + Doe = JohnDoe.
How can I 'unseal' the + method?
setMethod(+, signature(e1=character, e2=character), function(e1, e2) paste(e1, e2,
sep=) )
Error in setMethod(+, signature(e1 = character, e2 = character), :
the method for function + and signature e1=character, e2=character is
sealed and cannot be re-defined
Hi -- I think the two issues are that + is part of the Arith group
generic (?Methods, ?Arith) and that `+` (actually, members of the Ops
group) for primitive types dispatches directly without doing method
look-up. Personally I might
setClass(Character, contains=character)
Character - function(...) new(Character, ...)
setMethod(Arith, c(Character, Character), function(e1, e2) {
switch(.Generic,
+=Character(paste(e1, e2, sep=)),
stop(unhandled 'Arith' operator ', .Generic, '))
})
and then
Character(c(foo, bar)) + Character(baz)
[1] foobaz barbaz
Some might point to
`%+%` - function(e1, e2) paste(e1, e2, sep=)
foo %+% bar
[1] foobar
Martin
Cheers!!
Albert-Jan
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