Reference semantics

Methods that alter Container objects usually come in two versions providing either copy or reference semantics where the latter start with ‘ref_’ to note the reference semantic, for example, add() and ref_add().

Since reference semantics changes the original object, it can be used to save some typing.

co = container()

ref_add(co, a = 1)
ref_add(co, b = 2)

co
# [a = 1, b = 2]

Although these days this usually can be achieved equally easy using pipes.

co = container() |>
    add(a = 1)   |>
    add(b = 2)

Still there might be use cases, where it makes your life a bit easier. Consider the following silly example.

odds = container()
evens = container()
isOdd = function(x) {x %% 2 == 1}

res = sapply(1:10, function(i)
    if(isOdd(i)) ref_add(odds, i) else ref_add(evens, i)
)

odds
# [1L, 3L, 5L, 7L, 9L]
evens
# [2L, 4L, 6L, 8L, 10L]

Using reference semantics for it’s side effects (as in the above example) should be really done with care though and in most cases is probably best avoided as you risk introducing unnecessary coupling into your code.

Last but not least, reference semantics can make sense when you are dealing with very large objects to avoid copying. Although, these days R often is smart enough to only copy those parts of an objects, for which a copy is really needed (copy-on-modify).

To summarize, the container package does provide reference semantics, but it should be used with care.