type converters not being saved to workspace

(diverted to r-devel)

The problem seems to be rather that loading of the saved image takes place 
_after_ the packages are attached.  So nothing that the methods package does 
in its initialization will see the relevant type converters or other methods 
objects.

library(methods)

More generally, loading into .GlobalEnv will never cause the equivalent of 
cacheMetaData(.GlobalEnv).

It would be possible to hack the C code in main/saveload.c to generate a call 
to cacheMetaData under the right circumstances, but is that the best 
solution? 
Intuitively, it's the objects containing the method/class definitions that 
should trigger actions when they are loaded (emulating what happens when the 
corresponding setMethod or setClass function call takes place).  I.e., a load 
method for these classes of objects.  Possible?

It might be better, now that we're past feature freeze, to leave this as a 
"design infelicity" for the upcoming release.

Prof Brian Ripley wrote:

It is recommended that you use a package for this sort of thing.

When a package is loaded, the S4 methods it contains are merged into the 
metadata.  When the global environment is loaded, they are not.  Call 
'cacheMetaData(1)' to do so.

[This looks like a bug: cacheMetaData is called on .GlobalEnv in the 
startup code for package methods, but seems not to work when called from 
there.  I think this is because package methods is not at that point on the 
search path (the call is from .onLoad) and hence the coerce() generic is 
not visible to cacheMetaData.  If you have S4 code in a package, it will 
ensure that package methods is attached before your package is loaded.]

On Sun, 9 Apr 2006, Joseph Wang wrote:

Any one can explain why this happens or any work arounds?

setClass('foo')

[1] "foo"

setAs('foo', 'character', function(from) from)
showMethods('coerce')

Function "coerce":
from = "ANY", to = "array"
from = "ANY", to = "call"
from = "ANY", to = "character"
from = "ANY", to = "complex"
from = "ANY", to = "environment"
from = "ANY", to = "expression"
from = "ANY", to = "function"
from = "ANY", to = "integer"
from = "ANY", to = "list"
from = "ANY", to = "logical"
from = "ANY", to = "matrix"
from = "ANY", to = "name"
from = "ANY", to = "numeric"
from = "ANY", to = "single"
from = "ANY", to = "ts"
from = "ANY", to = "vector"
from = "ANY", to = "NULL"
from = "foo", to = "character"

q()

Save workspace image? [y/n/c]: y


(restart)

showMethods('coerce')

Function "coerce":
from = "ANY", to = "array"
from = "ANY", to = "call"
from = "ANY", to = "character"
from = "ANY", to = "complex"
from = "ANY", to = "environment"
from = "ANY", to = "expression"
from = "ANY", to = "function"
from = "ANY", to = "integer"
from = "ANY", to = "list"
from = "ANY", to = "logical"
from = "ANY", to = "matrix"
from = "ANY", to = "name"
from = "ANY", to = "numeric"
from = "ANY", to = "single"
from = "ANY", to = "ts"
from = "ANY", to = "vector"
from = "ANY", to = "NULL"
from = "NULL", to = "OptionalFunction"