list members can be accessed with partial name? Is this a feature?

Question

Consider this R code

> l = list(key = 1)
> l$k
[1] 1
> l$ke
[1] 1
> l[['k']]
NULL
> names(l)
[1] "key"

Does this mean that you can access a list member with $ and its partial name? I couldn't believe my eyes when I discovered this after a frustrating bug-hunting.

Is this a feature of R list? Is there a name for it? Is it possible to turn it off? This causes obvious troubles when you use it like a Python dict.

Answer 1

It's a feature that is meant to help in interactive mode. You can tighten it locally, see help(options) which has

 ‘warnPartialMatchArgs’: logical.  If true, warns if partial
      matching is used in argument matching.

 ‘warnPartialMatchAttr’: logical.  If true, warns if partial
      matching is used in extracting attributes via ‘attr’.

 ‘warnPartialMatchDollar’: logical.  If true, warns if partial
      matching is used for extraction by ‘$’.

Example:

R> l <- list(key = 1)
R> l$k
[1] 1
R> options("warnPartialMatchDollar"=TRUE)
R> l$k
[1] 1
Warning message:
In l$k : partial match of 'k' to 'key'
R> 

and you can further promote warnings to errors if you so choose (and that option is described on the same page).