[R] R-1.4.0 delay()

[Ray Brownrigg]

R-1.4.0 seems to have changed the way delay() works, or perhaps it is
the way library() works that nullifies the advantages of using delay()
in a package.

It seems that the process of loading a package evaluates each object
provided by that package, and so in particular, the delay()ed object is
evaluated and brought into memory.

For example generating a test example, where test/R/functions.s is:
test <- delay({attach(system.file("data/test.rda", package = "test")); test})

and test/data/test.rda is generated by:
test <- runif(5000000)
save(test, file="test/data/test.rda")

After installing this package (R INSTALL test) then invoking R, we get:

> library(test)

Attaching package `test':


	The following object(s) are masked _by_
file:/usr/lib/R/library/test/data/test.rda :

	 test 

> 
and there is a delay while the .rda file is read into memory.  This also
happens if the .rda file is external to the package (in /tmp/test.rda
for example).  Previously (before 1.4.0), the file was not read into
memory until the object test was referenced the first time.

I see in library(), there is the code fragment:

            env <- attach(NULL, name = pkgname)
            on.exit(do.call("detach", list(name = pkgname)))
            attr(env, "path") <- file.path(which.lib.loc, package)
            for (name in ls(loadenv, all = TRUE)) {
                val <- get(name, env = loadenv)
                rm(list = name, envir = loadenv, inherits = FALSE)
                if (typeof(val) == "closure" && identical(environment(val), 
                  loadenv)) 
                  environment(val) <- .GlobalEnv
                assign(name, val, env = env)
            }

which replaces (in 1.3.1):
            .Internal(lib.fixup(env, .GlobalEnv))

Could this be the cause?

I am reluctant to flag this as a bug, since delay() is documented
to be experimental.

Is there perhaps a workaround which will allow a package to install a
delayed reference?

I seem to remember that there may be another way of doing this
(reported by Duncan T-L?), which I will need to delve into if there is
no workaround.

Ray Brownrigg
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