I've noticed an increasing tendency for people to use '=' rather than
the older '<-' symbol. When '=' became available as an assignment
operator in S-PLUS in the late '90s my first reaction was to switch to
it as well. Brian Ripley warned me that it was not a good idea. As
usual he was right, but it took a couple of pretty serious
finger-burning episodes before I came fully around to his view.
There are three left assignment operators in S, and it's a good idea to
distinguish what they do.
a <<- b
assigns a value 'b' to an object 'a' in some parent environment
a <- b
assigns a value 'b' to an object 'a' in the current environment
a = b (inside the argument list of a function call)
potentially assigns a value 'b' to an object 'a' in the child
environment of the function. Lazy evaluation determines if it actually
happens or not.
You must use '=' for the third of these. If you choose to use it for
the second as well, as is allowed, there is a danger that you will
confuse the environment in which the assignment is actually made. It's
not a great danger, of course, but it can happen. In any case, it is a
good idea to use three separate operators for these three distinct
purposes, if nothing else as a clear visual reminder of what kind of
assignment is intended to take place.
I suspect the push towards using '=' instead of '<-' has two main
drivers:
1. the world is full of lazy typists
2. right now there seems to be a big influx of Matlab people into R, and
it makes them feel more at home.
Neither of these is much of a reason, I reckon.
Bill Venables
CSIRO Laboratories
PO Box 120, Cleveland, 4163
AUSTRALIA
Office Phone (email preferred): +61 7 3826 7251
Fax (if absolutely necessary): +61 7 3826 7304
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Home Phone: +61 7 3286 7700
mailto:[EMAIL PROTECTED]
http://www.cmis.csiro.au/bill.venables/
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