Duplicate-Method-Call.md

Duplicate Method Call

Introduction

Duplication occurs when two fragments of code look nearly identical, or when two fragments of code have nearly identical effects at some conceptual level. Reek implements a check for Duplicate Method Call.

Example

Here's a very much simplified and contrived example. The following method will report a warning:

def double_thing
  @other.thing + @other.thing
end

One quick approach to silence Reek would be to refactor the code thus:

def double_thing
  thing = @other.thing
  thing + thing
end

A slightly different approach would be to replace all calls in double_thing by calls to thing:

class Other
  def double_thing
    thing + thing
  end

  def thing
    @other.thing
  end
end

The approach you take will depend on balancing other factors in your code.

Current support in Reek

Reek's Duplicate Method Call detector checks for repeated identical method calls within any one method definition. This is intended to complement the checks performed by tools such as Flay and Simian.

Edge cases

Be aware that there are some edge cases like this code:

class Foo
  def bar(switch)
    case switch
    when :a
      ->(arg) { arg.call_me(:maybe); do_something }
    when :b
      ->(arg) { arg.call_me(:maybe); do_something_else }
    when :c
      ->(arg) { arg.call_me(:maybe); do_something_different }
    end
  end
end

Reek cannot reliably detect that each call's receiver is a different arg and will report:

[5, 7, 9]:DuplicateMethodCall: Foo#bar calls 'arg.call_me(:maybe)' 3 times

If you're running into this problem you can disable this smell detector for this method either via configuration:

---
DuplicateMethodCall:
  exclude:
    - 'Foo#bar'

or via source code comment:

class Foo
  # :reek:DuplicateMethodCall
  def bar(switch)
    # ....
  end
end

Configuration

Reek's Duplicate Method Call detector currently offers the Basic Smell Options, plus:

Option	Value	Effect
max_calls	integer	The maximum number of duplicate calls allowed within a method. Defaults to 1.
allow_calls	an array of strings or regular expressions	Ignores any context who matches it

Example configuration

Adjusting max_calls

Imagine code like this:

class Alfa
  def bravo
    charlie.delta
    charlie.delta
  end
end

This would report:

src.rb -- 1 warning: [4, 5]:DuplicateMethodCall: Alfa#bravo calls 'charlie.delta' 2 times

If you want to allow those double calls here you can disable it in 2 different ways:

1.) Via source code comment:

class Alfa
  # :reek:DuplicateMethodCall { max_calls: 2 }
  def bravo
    charlie.delta
    charlie.delta
  end
end

2.) Via configuration file:

DuplicateMethodCall:
  max_calls: 2

Note though that the latter way will set max_calls to 2 for all instances of the smell detector which might not be what you want - in this case you'll have to use source code comments.

Adjusting allow_calls

Imagine code like this:

class Alfa
  def bravo
    charlie.delta
    charlie.delta
    echo.foxtrot
    echo.foxtrot
  end
end

This would report:

src.rb -- 2 warnings: [4, 5]:DuplicateMethodCall: Alfa#bravo calls charlie.delta 2 times [6, 7]:DuplicateMethodCall: Alfa#bravo calls echo.foxtrot 2 times

So let's say you're ok with the echo.foxtrot calls you can stop reporting them like this:

1.) Via source code comment:

class Alfa
  # :reek:DuplicateMethodCall { allow_calls: ['echo.foxtrot'] }
  def bravo
    charlie.delta
    charlie.delta
    echo.foxtrot
    echo.foxtrot
  end
end

2.) Via configuration file:

DuplicateMethodCall:
  allow_calls:
  - 'echo.foxtrot'

Note though that the latter way will allow those calls across your source code which might not be what you want. In this case you'll have to use source code comments.