You can do stuff like this now
test = instruments$new()
test$addCurrency(primary_id = USD, multipler = .3, foo = "blarney")
test$addCurrency(primary_id = EUR, multipler = 1.3, foo = "baloney")
test$getCurrency(primary_id = EUR)
test$addStock(primary_id = ETX, currency = USD)
test$getStock(ETX)
#<stock>
# Public:
# clone: function (deep = FALSE)
# currency: NULL
# identifiers: currency, R6
# initialize: function (primary_id, identifiers = NULL, multiplier = 1, tick_size = 0.01,
# multiplier: 1
# primary_id: primary_id
# tick_size: 0.01
# type: NULL