loom v0.0.9 → Overview → Loom → PNCounter

Loom.PNCounter

Positive-negative counters

PNCounters are counters that are capable of incrementing and decrementing. They are useful for like counters, where a user may like and then unlike something in succession.

They are not delta-CRDT’s, as they are rather lightweight in general. A delta- CRDT implementation would just return the latest value for an actor.

They do, however, implement the CRDT protocol, and can be coposed into larger CRDT datastructures.

Summary
↑

dec(c, actor, int \\ 1)

Decrement a counter on behalf of the actor
inc(c, actor, int \\ 1)

Increment a counter on behalf of the actor
join(pncounter, pncounter)

Joins 2 counters together
new()

Instantiate a new PNCounter. Starts at 0
new(opts)

Instantiate a new PNCounter with previous values
value(pncounter)

Gets a natural value for the counter

Types ↑

actor :: term

dot :: {actor, pos_integer}

t :: %Loom.PNCounter{p: %{actor => pos_integer}, n: %{actor => pos_integer}}

Functions

dec(c, actor, int \\ 1)
(function) # ↑

Specs:

Decrement a counter on behalf of the actor.

iex> alias Loom.PNCounter, as: Counter
iex> Counter.new
...> |> Counter.dec(:a, 1)
...> |> Counter.dec(:a, 29)
...> |> Counter.value
-30
iex> Counter.new
...> |> Counter.inc(:a, 1)
...> |> Counter.dec(:a, 1)
...> |> Counter.value
0
inc(c, actor, int \\ 1)
(function) # ↑

Specs:

Increment a counter on behalf of the actor.

iex> alias Loom.PNCounter, as: Counter
iex> Counter.new
...> |> Counter.inc(:a, 1)
...> |> Counter.inc(:a, 29)
...> |> Counter.value
30
join(pncounter, pncounter)
(function) # ↑

Specs:

  • join(t, t) :: t

Joins 2 counters together.

iex> alias Loom.PNCounter, as: Counter
iex> ctr1 = Counter.new |> Counter.inc(:a) |> Counter.dec(:a, 10)
iex> ctr2 = Counter.new |> Counter.dec(:b) |> Counter.inc(:b, 5)
iex> Counter.join(ctr1,ctr2) |> Counter.value
-5
new()
(function) # ↑

Specs:

  • new :: t

Instantiate a new PNCounter. Starts at 0.

iex> Loom.PNCounter.new |> Loom.PNCounter.value
0
new(opts)
(function) # ↑

Specs:

  • new([{:values, [{actor, {non_neg_integer, non_neg_integer}}]}]) :: t

Instantiate a new PNCounter with previous values.

iex> alias Loom.PNCounter, as: Counter
iex> values = [a: {10,0}, b: {5,5}, c: {37,5}]
iex> Counter.new(values: values) |> Counter.value
42
value(pncounter)
(function) # ↑

Specs:

  • value(t) :: integer

Gets a natural value for the counter.

For counters, it is an integer.