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

Relationships & Source Files
Super Chains via Extension / Inclusion / Inheritance
Class Chain: self, Base
Instance Chain: self, Base
Inherits:	Base Object Base RuboCop::Cop::Performance::ChainArrayAllocation
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

ALWAYS_RETURNS_NEW_ARRAY =

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

# File 'lib/rubocop/cop/performance/chain_array_allocation.rb', line 35
```
%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!

# File 'lib/rubocop/cop/performance/chain_array_allocation.rb', line 43
```
%i[collect compact flatten map reject
reverse rotate select shuffle sort uniq].to_set.freeze
```

MSG =
# File 'lib/rubocop/cop/performance/chain_array_allocation.rb', line 48

'Use unchained `%<method>s` and `%<second_method>s!` ' \
'(followed by `return array` if required) instead of chaining ' \
'`%<method>s...%<second_method>s`.'

RETURNS_NEW_ARRAY =
# File 'lib/rubocop/cop/performance/chain_array_allocation.rb', line 46
```
(ALWAYS_RETURNS_NEW_ARRAY + RETURNS_NEW_ARRAY_WHEN_NO_BLOCK).freeze
```
RETURNS_NEW_ARRAY_WHEN_NO_BLOCK =

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

# File 'lib/rubocop/cop/performance/chain_array_allocation.rb', line 31
```
%i[zip product].to_set.freeze
```
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]
# File 'lib/rubocop/cop/performance/chain_array_allocation.rb', line 28
```
%i[first last pop sample shift].to_set.freeze
```

Instance Method Summary

#on_send(node)
#enumerable_select_method?(node) ⇒ Boolean private

Instance Method Details

#enumerable_select_method?(node) ⇒ `Boolean` (private)

[ GitHub ]

# File 'lib/rubocop/cop/performance/chain_array_allocation.rb', line 73


def enumerable_select_method?(node)
  # NOTE: `QueryMethods#select` in Rails accepts positional arguments, whereas `Enumerable#select` does not.
  #        This difference can be utilized to reduce the knowledge requirements related to `select`.
  (node.block_type? || node.numblock_type?) && node.send_node.arguments.empty?
end

#on_send(node)