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In the code below, LETTERS and letters are global, or in the global search path and reachable through another package (same thing!)
> LETTERS [1] "A" "B" "C" "D" "E" "F" "G" "H" "I" "J" "K" "L" "M" "N" "O" "P" "Q" "R" "S" [20] "T" "U" "V" "W" "X" "Y" "Z" > letters [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p" "q" "r" "s" [20] "t" "u" "v" "w" "x" "y" "z" > ls() character(0) > a <- "1 2 3" > ls() [1] "a" > rm(a) > ls() character(0) >
677
Functions can access global variables and modify them. Modifying global variables in a function is considered poor programming practice.
A global variable can have no access control. It can not be limited to some parts of the program. Using global variables causes very tight coupling of code. Using global variables causes namespace pollution.
The simplest way to avoid globals all together is to simply pass your variables using function arguments. As you can see, the $productData array from the controller (via HTTP request) goes through different layer: The controller receives the HTTP request. The parameters are passed to the model.
For the same reason it doesn't list all the exported functions in all the attached packages (from ?ls):
By default, the environment of the call to 'ls' or 'objects' is used.
Specify the environment that contains LETTERS and ls will print it's name.
# LETTERS is in there somewhere...
sapply(search(),ls)
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