Count, size, length…too many choices in Ruby?

Question

I can\'t seem to find a definitive answer on this and I want to make sure I understand this to the \"n\'th level\" :-)

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Answer 1

In most cases (e.g. Array or String) size is an alias for length.

count normally comes from Enumerable and can take an optional predicate block. Thus enumerable.count {cond} is [roughly] (enumerable.select {cond}).length -- it can of course bypass the intermediate structure as it just needs the count of matching predicates.

Note: I am not sure if count forces an evaluation of the enumeration if the block is not specified or if it short-circuits to the length if possible.

Edit (and thanks to Mark's answer!): count without a block (at least for Arrays) does not force an evaluation. I suppose without formal behavior it's "open" for other implementations, if forcing an evaluation without a predicate ever even really makes sense anyway.