Packages
credo
1.7.10
1.7.19
1.7.18
1.7.17
1.7.16
1.7.15
1.7.14
1.7.13
1.7.12
1.7.11
1.7.10
1.7.9
1.7.8
1.7.7
1.7.7-rc.0
1.7.6
1.7.5
1.7.4
1.7.3
1.7.2
1.7.2-rc.4
1.7.2-rc.3
1.7.2-rc.2
1.7.2-rc.1
1.7.2-rc.0
1.7.1
1.7.0
1.7.0-rc.2
1.7.0-rc.1
1.6.7
1.6.6
1.6.5
1.6.4
1.6.3
1.6.2
1.6.1
1.6.0
1.6.0-rc.1
1.6.0-rc.0
1.5.6
1.5.5
1.5.4
1.5.3
1.5.2
1.5.1
1.5.0
1.5.0-rc.5
1.5.0-rc.4
1.5.0-rc.3
1.5.0-rc.2
1.5.0-rc.1
1.4.1
1.4.0
1.4.0-rc.2
1.4.0-rc.1
1.3.2
1.3.1
1.3.0
1.3.0-rc3
1.3.0-rc2
1.3.0-rc1
1.2.3
1.2.2
1.2.1
1.2.0
1.2.0-rc4
1.2.0-rc3
1.2.0-rc2
1.2.0-rc1
1.1.5
1.1.4
1.1.3
1.1.2
1.1.1
1.1.0
1.1.0-rc3
1.1.0-rc2
1.1.0-rc1
1.0.5
1.0.4
1.0.3
1.0.2
1.0.1
1.0.1-rc1
1.0.0
1.0.0-rc1
0.10.2
0.10.1
0.10.0
0.9.3
0.9.2
0.9.1
0.9.0
0.9.0-rc8
0.9.0-rc7
0.9.0-rc6
0.9.0-rc5
0.9.0-rc4
0.9.0-rc3
0.9.0-rc2
0.9.0-rc1
0.8.10
0.8.9
0.8.8
0.8.7
0.8.6
0.8.5
0.8.4
0.8.3
0.8.2
0.8.1
0.8.0
0.8.0-rc7
0.8.0-rc6
0.8.0-rc5
0.8.0-rc4
0.8.0-rc3
0.8.0-rc2
0.8.0-rc1
0.7.4
0.7.3
0.7.2
0.7.1
0.7.0
0.6.1
0.6.0
0.6.0-rc2
0.6.0-rc1
0.5.3
0.5.2
0.5.1
0.5.0
0.4.14
0.4.13
0.4.12
0.4.11
0.4.10
0.4.10-dev
0.4.9
0.4.8
0.4.7
0.4.6
0.4.5
0.4.4
0.4.3
0.4.2
0.4.1
0.4.0
0.4.0-beta5
0.4.0-beta4
0.4.0-beta3
0.4.0-beta2
0.4.0-beta1
0.3.13
0.3.12
0.3.11
0.3.10
0.3.9
0.3.8
0.3.7
0.3.6
0.3.5
0.3.4
0.3.3
0.3.2
0.3.1
0.3.0
0.3.0-dev2
0.3.0-dev
0.2.6
0.2.5
0.2.4
0.2.3
0.2.2
0.2.1
0.2.0
0.1.10
0.1.9
0.1.8
0.1.7
0.1.6
0.1.5
0.1.4
0.1.3
0.1.2
0.1.1
0.1.0
0.0.1-dev
A static code analysis tool with a focus on code consistency and teaching.
Current section
Files
Jump to
Current section
Files
lib/credo/check/refactor/append_single_item.ex
defmodule Credo.Check.Refactor.AppendSingleItem do
use Credo.Check,
id: "EX4002",
base_priority: :low,
tags: [:controversial],
explanations: [
check: """
When building up large lists, it is faster to prepend than
append. Therefore: It is sometimes best to prepend to the list
during iteration and call Enum.reverse/1 at the end, as it is quite
fast.
Example:
list = list_so_far ++ [new_item]
# refactoring it like this can make the code faster:
list = [new_item] ++ list_so_far
# ...
Enum.reverse(list)
"""
]
@doc false
@impl true
def run(%SourceFile{} = source_file, params) do
issue_meta = IssueMeta.for(source_file, params)
Credo.Code.prewalk(source_file, &traverse(&1, &2, issue_meta))
end
# [a] ++ b is OK
defp traverse({:++, _, [[_], _]} = ast, issues, _issue_meta) do
{ast, issues}
end
# a ++ [b] is not
defp traverse({:++, meta, [_, [_]]} = ast, issues, issue_meta) do
{ast, [issue_for(issue_meta, meta[:line], :++) | issues]}
end
defp traverse(ast, issues, _issue_meta) do
{ast, issues}
end
defp issue_for(issue_meta, line_no, trigger) do
format_issue(
issue_meta,
message:
"Appending a single item to a list is inefficient, use `[head | tail]` notation (and `Enum.reverse/1` when order matters).",
trigger: trigger,
line_no: line_no
)
end
end