andypike/rectify

Feature Envy occurs when a code fragment references another object more often than it references itself, or when several clients do the same series of manipulations on a particular type of object.

Feature Envy reduces the code's ability to communicate intent: code that "belongs" on one class but which is located in another can be hard to find, and may upset the "System of Names" in the host class.

Feature Envy also affects the design's flexibility: A code fragment that is in the wrong class creates couplings that may not be natural within the application's domain, and creates a loss of cohesion in the unwilling host class.

Feature Envy often arises because it must manipulate other objects (usually its arguments) to get them into a useful form, and one force preventing them (the arguments) doing this themselves is that the common knowledge lives outside the arguments, or the arguments are of too basic a type to justify extending that type. Therefore there must be something which 'knows' about the contents or purposes of the arguments. That thing would have to be more than just a basic type, because the basic types are either containers which don't know about their contents, or they are single objects which can't capture their relationship with their fellows of the same type. So, this thing with the extra knowledge should be reified into a class, and the utility method will most likely belong there.

Example

Running Reek on:

class Warehouse
  def sale_price(item)
    (item.price - item.rebate) * @vat
  end
end

would report:

Warehouse#total_price refers to item more than self (FeatureEnvy)

since this:

(item.price - item.rebate)

belongs to the Item class, not the Warehouse.

A Long Parameter List occurs when a method has a lot of parameters.

Example

Given

class Dummy
  def long_list(foo,bar,baz,fling,flung)
    puts foo,bar,baz,fling,flung
  end
end

Reek would report the following warning:

test.rb -- 1 warning:
  [2]:Dummy#long_list has 5 parameters (LongParameterList)

A common solution to this problem would be the introduction of parameter objects.

A Long Yield List occurs when a method yields a lot of arguments to the block it gets passed.

Example

class Dummy
  def yields_a_lot(foo,bar,baz,fling,flung)
    yield foo,bar,baz,fling,flung
  end
end

Reek would report the following warning:

test.rb -- 1 warning:
  [4]:Dummy#yields_a_lot yields 5 parameters (LongYieldList)

A common solution to this problem would be the introduction of parameter objects.

Feature Envy occurs when a code fragment references another object more often than it references itself, or when several clients do the same series of manipulations on a particular type of object.

Feature Envy reduces the code's ability to communicate intent: code that "belongs" on one class but which is located in another can be hard to find, and may upset the "System of Names" in the host class.

Feature Envy also affects the design's flexibility: A code fragment that is in the wrong class creates couplings that may not be natural within the application's domain, and creates a loss of cohesion in the unwilling host class.

Feature Envy often arises because it must manipulate other objects (usually its arguments) to get them into a useful form, and one force preventing them (the arguments) doing this themselves is that the common knowledge lives outside the arguments, or the arguments are of too basic a type to justify extending that type. Therefore there must be something which 'knows' about the contents or purposes of the arguments. That thing would have to be more than just a basic type, because the basic types are either containers which don't know about their contents, or they are single objects which can't capture their relationship with their fellows of the same type. So, this thing with the extra knowledge should be reified into a class, and the utility method will most likely belong there.

Example

Running Reek on:

class Warehouse
  def sale_price(item)
    (item.price - item.rebate) * @vat
  end
end

would report:

Warehouse#total_price refers to item more than self (FeatureEnvy)

since this:

(item.price - item.rebate)

belongs to the Item class, not the Warehouse.

Classes and modules are the units of reuse and release. It is therefore considered good practice to annotate every class and module with a brief comment outlining its responsibilities.

Example

Given

class Dummy
  # Do things...
end

Reek would emit the following warning:

test.rb -- 1 warning:
  [1]:Dummy has no descriptive comment (IrresponsibleModule)

Fixing this is simple - just an explaining comment:

# The Dummy class is responsible for ...
class Dummy
  # Do things...
end

An Uncommunicative Variable Name is a variable name that doesn't communicate its intent well enough.

Poor names make it hard for the reader to build a mental picture of what's going on in the code. They can also be mis-interpreted; and they hurt the flow of reading, because the reader must slow down to interpret the names.

An Uncommunicative Variable Name is a variable name that doesn't communicate its intent well enough.

Poor names make it hard for the reader to build a mental picture of what's going on in the code. They can also be mis-interpreted; and they hurt the flow of reading, because the reader must slow down to interpret the names.