How to understand packages, namespaces, environments

[Alexander Stoddard]

Subject: Re: [Rd] How to understand packages, namespaces, environments

Does saying the following load package 'foo' into its own

environment ?

 > library(foo)

[Duncan Murdoch]

This loads some of the (name, object) pairs from the package into two
environments:  the public one the user can see, and the
namespace one that the code in the package can see.  They're
related, you don't get two copies of the objects.

That's interesting-- I thought there really were two copies. In my debug
package, I've taken the approach of changing both copies.

[Alexander Stoddard]

Subject: Re: [Rd] How to understand packages, namespaces, environments

Does saying the following load package 'foo' into its own

environment ?

library(foo)

[Duncan Murdoch]

This loads some of the (name, object) pairs from the package into two
environments:  the public one the user can see, and the
namespace one that the code in the package can see.  They're
related, you don't get two copies of the objects.

That's interesting-- I thought there really were two copies. In my debug
package, I've taken the approach of changing both copies. Is one of the
copies a "master", and the other one something like an activeBinding?
Can I get away with changing just one of them?

On Mon, 9 May 2005 Mark.Bravington@csiro.au wrote:

[Alexander Stoddard]

Subject: Re: [Rd] How to understand packages, namespaces, environments

Does saying the following load package 'foo' into its own

environment ?

library(foo)

[Duncan Murdoch]

This loads some of the (name, object) pairs from the package into two
environments:  the public one the user can see, and the
namespace one that the code in the package can see.  They're
related, you don't get two copies of the objects.

That's interesting-- I thought there really were two copies. In my debug
package, I've taken the approach of changing both copies. Is one of the
copies a "master", and the other one something like an activeBinding?
Can I get away with changing just one of them?

Duncan is wrong here (or misquoted).  

Loading a package with a namespace 
loads all the objects in the package (possibly as promises) into the 
namespace environment.  Then some are copied (using assign) to the 
package environment.  Since like most R copies this is really 
copy-on-change you do not get a real copy (nor force a promise) until use.

See ?fixInNamespace for explicit statements about this.  There can be 
more than two copies, since importing also `copies', as does S3 method 
registration (the latter does sometimes force promises).