Errors or warnings for non-existent data

Good Evening

Is there a setting that I can change in R so that I get either a warning or an error message if I reference  non-existent data in a data frame?  For example I get no warning or error message with the following:

Use specific methods of indexing as a data frame: [ not $.  That $ 
returns NULL for a non-existent list component is deliberate design, and 
as the help says

      Note that there is no ?data.frame? method for ?$?, so ?x$name?
      uses the default method which treats ?x? as a list.  There is a
      replacement method which checks ?value? for the correct number of
      rows, and replicates it if necessary.

E.g.

 > df0["w"]
Error in `[.data.frame`(df0, "w") : undefined columns selected

Other bad habits to get out of are not using your space bar, and using = 
for assignment in public code: your second line is very hard for humans 
to parse compared to

df0 <- data.frame(x = rnorm(1000), y = rnorm(1000))

the cbind() being a waste of time (it forms a matrix and data.frame then 
splits it up into columns).

set.seed(2013)
df0=data.frame(cbind(x=rnorm(1000),y=rnorm(1000)))
df0$z=df0$w
head(df0)

             x           y
1 -0.09202453  1.51179695
2  0.78901912 -0.60084547
3 -0.66744232 -0.02180077
4  1.36061149 -0.74909011
5  1.50768816 -2.25128946
6 -2.60754997  0.43708800

Thanks
Joe

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Brian D. Ripley,                  ripley at stats.ox.ac.uk
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