On 12-03-07 10:37 AM, Duncan Murdoch wrote:
On 12-03-07 9:52 AM, Richard Cotton wrote:
Even for an extremely simple instance of a reference class
x<- setRefClass("x")
y<- x$new()
calling the internal inspect function
.Internal(inspect(y))
produces enough output that it takes several minutes to print to the
console. (Actually I gave up and terminated the command after ~10
mins. It isn't clear whether the output would eventually complete.)
Are reference classes really so complicated inside, or is this a bug?
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If you look at the output, you'll see it's looping. When I hit Esc, I
saw that .self is an S4SXP with an attribute .xData which is an
environment containing the same .self, ad infinitum.
So I'd say it's a bug in inspect(). It can handle the case of an
environment holding itself, but I think it was written before S4SXPs
contained themselves, and it looks like it's not checking for that.
I'll take a look if someone else doesn't get there first...
There are a couple of optional arguments to inspect that let you avoid
this infinite recursion, e.g.
.Internal(inspect(y, 5))
will limit the recursion depth to 5, and that's sufficient for this example.
It would be possible to put loop detection into the function, or default
to a finite depth, but I'd rather not mess it up: keeping debugging
aids simple but powerful seems like a good idea to me. You can always
hit Esc to stop the display if it goes into a loop, then set a depth
limit as above.
Duncan Murdoch
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