track (version 1.1.9)

track.future: Potential future features of the track package

Description

Potential future features of the track package, in some vague order of feasibility and priority ('easy', 'medium' and 'hard' are an estimate of design and coding difficulty):

Example of the "double-get" when assigning a subset (using the example from the help page for makeActiveBinding). Note that it works correctly, but retrieving the object twice seems unneccessary and could be slow with very large objects.

> f <- local( {
+     x <- 1
+     function(v) {
+        if (missing(v))
+            cat("get\n")
+        else {
+            cat("set\n")
+            x <<- v="" +="" }="" x="" })=""> makeActiveBinding("X", f, .GlobalEnv)
NULL
> bindingIsActive("X", .GlobalEnv)
[1] TRUE
> X
get
[1] 1
> X <- 2
set
> X
get
[1] 2
>
> X[1]
get
[1] 2
> X[2] <- 1 # 'X' is fetched twice
get
get
set
> X
get
[1] 2 1
>

See Also

Overview and design of the track package.

Examples

# Example (transcript shown above) of how subset-assignment
# results in two retrievals when the object is an active binding.
f <- local( {
    x <- 1
    function(v) {
       if (missing(v)) {
           cat("get\n")
       } else {
           cat("set\n")
           x <<- v
       }
       x
    }
})
makeActiveBinding("X", f, .GlobalEnv)
bindingIsActive("X", .GlobalEnv)
X
X <- 2
X
X[1]
X[2] <- 1 # 'X' is fetched twice
X