Class: RuboCop::Cop::Performance::ChainArrayAllocation

Inherits:
Base
  • Object
show all
Defined in:
lib/rubocop/cop/performance/chain_array_allocation.rb

Overview

Identifies usages of ‘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.

Examples:

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

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

Constant Summary collapse

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]

%i[first last pop sample shift].to_set.freeze
RETURNS_NEW_ARRAY_WHEN_NO_BLOCK =

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

%i[zip product].to_set.freeze
ALWAYS_RETURNS_NEW_ARRAY =

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

%i[* + - collect compact drop
drop_while flatten map reject
reverse rotate select shuffle sort
take take_while transpose uniq
values_at |].to_set.freeze
HAS_MUTATION_ALTERNATIVE =

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

%i[collect compact flatten map reject
reverse rotate select shuffle sort uniq].to_set.freeze
RETURNS_NEW_ARRAY = 
(ALWAYS_RETURNS_NEW_ARRAY + RETURNS_NEW_ARRAY_WHEN_NO_BLOCK).freeze
MSG = 
'Use unchained `%<method>s` and `%<second_method>s!` ' \
'(followed by `return array` if required) instead of chaining ' \
'`%<method>s...%<second_method>s`.'

Instance Method Summary collapse

Instance Method Details

#on_send(node) ⇒ Object 



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# File 'lib/rubocop/cop/performance/chain_array_allocation.rb', line 60

def on_send(node)
  chain_array_allocation?(node) do |fm, sm|
    return if node.each_descendant(:send).any? { |descendant| descendant.method?(:lazy) }
    return if node.method?(:select) && !enumerable_select_method?(node.receiver)

    range = node.loc.selector.begin.join(node.source_range.end)

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