class RuboCop::Cop::Performance::ChainArrayAllocation

This cop is used to identify usages of @example

# bad
array = ["a", "b", "c"]
array.compact.flatten.map { |x| x.downcase }

Each of these methods (`compact`, `flatten`, `map`) will generate a new intermediate array that is promptly thrown away. Instead it is faster to mutate when we know it's safe.

@example

# good.
array = ["a", "b", "c"]
array.compact!
array.flatten!
array.map! { |x| x.downcase }
array

Constants

ALWAYS_RETURNS_NEW_ARRAY

These methods ALWAYS return a new array after they're called it's safe to mutate the the resulting array

HAS_MUTATION_ALTERNATIVE

These methods have a mutation alternative. For example :collect can be called as :collect!

MSG
RETURNS_NEW_ARRAY
RETURNS_NEW_ARRAY_WHEN_NO_BLOCK

These methods return a new array only when called without a block.

RETURN_NEW_ARRAY_WHEN_ARGS

These methods return a new array but only sometimes. They must be called with an argument. For example:

[1,2].first    # => 1
[1,2].first(1) # => [1]

Public Instance Methods

on_send(node) click to toggle source
# File lib/rubocop/cop/performance/chain_array_allocation.rb, line 64
def on_send(node)
  chain_array_allocation?(node) do |fm, sm|
    return if node.each_descendant(:send).any? { |descendant| descendant.method?(:lazy) }

    range = range_between(node.loc.dot.begin_pos, node.source_range.end_pos)

    add_offense(range, message: format(MSG, method: fm, second_method: sm))
  end
end