Limit use of conditional modifiers to short, simple cases.

Co-authored-by: Richard Newman <[email protected]>

Author: MatheusRich

ruby/README.md

@@ -2,8 +2,12 @@
 
 [Sample 1](sample_1.rb) [Sample 2](sample_2.rb)
 
+> [!TIP]
+> Click on the linked pull request, commit, or the guideline itself to read more
+> detailed explanations with examples and reasoning behind these recommendations.
+
 - Use [standard]
-- Avoid conditional modifiers (lines that end with conditionals). [36491dbb9]
+- [Limit use of conditional modifiers to short, simple cases.](./conditional_modifiers.md)
 - Avoid multiple assignments per line (`one, two = 1, 2`). [#109]
 - Avoid organizational comments (`# Validations`). [#63]
 - Avoid ternary operators (`boolean ? true : false`). Use multi-line `if`

ruby/conditional_modifiers.md

@@ -0,0 +1,86 @@
+# 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:
+
+```ruby
+do_later if async?
+```
+
+The example above can read more naturally than:
+
+```rb
+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:
+
+```ruby
+# 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.
+
+```ruby
+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.
+
+```rb
+# 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:
+
+```rb
+def action
+  return do_nothing if chill?
+
+  destroy_all
+end
+```