More strange [[ behaviour

Hi,

setClass("MyList", "list")

[1] "MyList"

a <- new("MyList")
a

An object of class "MyList"
list()

setMethod("[[", "MyList", function(x, i, j, ...) cat("Just testing\n"))
a[[]]

Just testing

a[[1]]

Just testing

a[[a=1]]

Just testing

a[[b=1]]

Just testing
...

a[[v=1]]

Just testing

a[[w=1]]

Just testing

a[[x=1]]

Error in a[[x = 1]] : subscript out of bounds

a[[y=1]]

Just testing

a[[z=1]]

Just testing

Can someone explain me why the "[[x=1]]" case is treated differently?

On 10/2/2006 3:21 PM, Herve Pages wrote:

a[[x=1]]

Error in a[[x = 1]] : subscript out of bounds

Indexing is a function call, with arguments x, i, j, ... .  If you use
y=1, you're setting something in the "..." part of the arg list.  If
you say x=1, you're setting the first arg, but because a[[x=1]] is the
same as "[["(a, x=1), it is going to evaluate it as "[["(x=1, i=a) and
try to index 1 by a instead of a by 1.