Limit-use-of-conditional-modifiers-to-short-simple-cases.md

Limit use of conditional modifiers to short, simple cases

Conditional modifiers (i.e., if or unless at the end of a line) can be surprising when they appear on long or complex lines. The reader might not see them while scanning the code.

So, prefer to use them only for short, simple cases. For example:

do_later if async?

The example above can read more naturally than:

if async?
  do_later
end

Complex conditions

However, if the line is too long (around 80 characters) or complex (e.g., an if with multiple conditions like if a && b) prefer the multi-line form:

# Avoid
block_access! if signed_in? && !current_user.active?

# Prefer
if signed_in? && !current_user.active?
  block_access!
end

There might be cases where the conditional modifier work well with multiple conditions, so use your best judgment.

An opportunity to refactor

If the conditions are related, consider extracting a method that groups them. This might allow you to use the conditional modifier form again.

def inactive_user?
  signed_in? && !current_user.active?
end

block_access! if inactive_user?

Conditional modifiers feel informal

The modifier form of conditionals can feel more casual than the multi-line form. Conversely, the multi-line form draws attention to the conditional and the code that follows it. Use this to your advantage when you want to emphasize the conditional and the code that follows it.

# Avoid
def action
  return destroy_all if really?

  do_nothing
end

# Prefer
def action
  if really?
    destroy_all
  else
    do_nothing
  end
end

You can also refactor the code so the less destructive action uses a conditional modifier, which pairs well with the informal feel of the modifier form:

def action
  return do_nothing if chill?

  destroy_all
end

References

• You can see further discussion of this guideline here: #738