1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
|
# frozen_string_literal: true
module RuboCop
module Cop
module Performance
# 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
class ChainArrayAllocation < Cop
include RangeHelp
# 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]
#
RETURN_NEW_ARRAY_WHEN_ARGS = ':first :last :pop :sample :shift '
# These methods return a new array only when called without a block.
RETURNS_NEW_ARRAY_WHEN_NO_BLOCK = ':zip :product '
# These methods ALWAYS return a new array
# after they're called it's safe to mutate the the resulting array
ALWAYS_RETURNS_NEW_ARRAY = ':* :+ :- :collect :compact :drop '\
':drop_while :flatten :map :reject ' \
':reverse :rotate :select :shuffle :sort ' \
':take :take_while :transpose :uniq ' \
':values_at :| '
# These methods have a mutation alternative. For example :collect
# can be called as :collect!
HAS_MUTATION_ALTERNATIVE = ':collect :compact :flatten :map :reject '\
':reverse :rotate :select :shuffle :sort '\
':uniq '
MSG = 'Use unchained `%<method>s!` and `%<second_method>s!` '\
'(followed by `return array` if required) instead of chaining '\
'`%<method>s...%<second_method>s`.'
def_node_matcher :flat_map_candidate?, <<~PATTERN
{
(send (send _ ${#{RETURN_NEW_ARRAY_WHEN_ARGS}} {int lvar ivar cvar gvar}) ${#{HAS_MUTATION_ALTERNATIVE}} $...)
(send (block (send _ ${#{ALWAYS_RETURNS_NEW_ARRAY} }) ...) ${#{HAS_MUTATION_ALTERNATIVE}} $...)
(send (send _ ${#{ALWAYS_RETURNS_NEW_ARRAY + RETURNS_NEW_ARRAY_WHEN_NO_BLOCK}} ...) ${#{HAS_MUTATION_ALTERNATIVE}} $...)
}
PATTERN
def on_send(node)
flat_map_candidate?(node) do |fm, sm, _|
range = range_between(
node.loc.dot.begin_pos,
node.source_range.end_pos
)
add_offense(
node,
location: range,
message: format(MSG, method: fm, second_method: sm)
)
end
end
end
end
end
end
|
