Allow new_env() to create an environment with a specified parent

[lionel-]

Hello,

This is a small change to have a more useful way of creating environments with Rcpp.

[eddelbuettel]

Thanks for the contribution. Do you have a usage example? And/or test case we can add to the unit tests?

[lionel-]

For example you can capture the calling environment to your cpp function from its R wrapper with parent.frame(). Then you create a new environment (call it my_env) that has the calling env as parent. You can put several things in there, knowing that it won't have side effects, and then evaluate some R code with Rf_eval() in this environment. Variable lookup will first take place in my_env, then in the calling env, then its parent and so on.

I could add a test that checks that the parent is the correct one if you want.

[eddelbuettel]

Yes, I would really appreciate a few (simple) tests as part of the PR.

[lionel-]

Here you go.

[lionel-]

wait a minute, I made a mistake in there

why did the test not fail? :/

[lionel-]

ok, I should have used checkIdentical()

should be good now

[eddelbuettel]

Looks good. Odd indeed that checkEquals() failed there.

[lionel-]

Thanks for your quick review!