Make packages loadable via import

[klmr]

Add a mechanism to make installed packages available via import.

This would have the following advantages over library:

• Uniform API for accessing library code

• Doesn’t clutter the search path by default – encourages better style

• Allows adapting the name for accessing packages (instead of having hard-coded pkg_name::)

• Supports loading and using packages locally only; consider:

  frob = function (args) {
      import(package = 'pkg', attach = TRUE)
      …
  }

  Now pkg is attached, but only inside frob – just like normal modules, but unlike loading a package via library.

[klmr]

Hmm.

• import(package = '…'), or
• import_package('…')

… or something else entirely?

[gaborcsardi]

import_package is easier to search for, on Github and elsewhere, so I like that better.

[klmr]

Loading and dispatching the documentation attached to the package is tricky. I’ll omit this for now and I’ve opened an own issue for that (#54).

The prototype I’m currently working on probably has additional problems concerning the dispatch of S4 methods and operators. However, this seems to work in my ad-hoc tests. I’ll therefore release the preliminary prototype now in order to get feedback from real-life testing.