Code Documentation

Overview

In this guide, you can learn about Mongoid's code documentation conventions. If you have a suggestion to improve the API documentation or introduce a new feature, you can use this guide to help you format your documentation.

Mongoid uses a variation of YARD, a Ruby documentation tool, for its code documentation.

Structure

Modules: All class and module definitions must be preceded by a documentation comment.
```
# This is the documentation for the class. It's amazing# what they do with corrugated cardboard these days.class CardboardBox
```
Methods: All method definitions must be preceded by a documentation comment. Use @param, @yield, and @return to specify inputs and output. To learn more, see the Type Declaration section.
```
# Turn a person into whatever they'd like to be.## @param [ Person ] person The human to transmogrify.## @return [ Tiger ] The transmogrified result.def transmogrify(person)
```
Errors: Use @raise to describe errors specific to the method.
```
# @raise [ Errors::Validations ] If validation failed.def validate!
```
Private Methods: Private methods must be documented unless they are so brief and straightforward that it is obvious what they do. Note that, for example, a method might be brief and straightforward but the type of its parameter may not be obvious, in which case the parameter must be appropriately documented.
```
private
# Documentation is optional here.def do_something_obvious
```
API Private: Classes and public methods which are not intended for external usage must be marked @api private. This macro does not require a comment.

Note that, because Mongoid's modules are mixed into application classes, private visibility of a method does not necessarily indicate its status as an API private method.
```
# This is an internal-only method.## @api privatedef dont_call_me_from_outside
```
Notes and TODOs: Use @note to explain caveats, edge cases, and behavior which may surprise users. Use @todo to record follow-ups and suggestions for future improvement.
```
# Clear all stored data.## @note This operation deletes data in the database.# @todo Refactor this method for performance.def erase_data!
```
Deprecation: Use the @deprecated macro to indicate deprecated functionality. This macro does not require a comment.
```
# This is how we did things back in the day.## @deprecateddef the_old_way
```

Formatting

Line Wrapping: Use double-space indent when wrapping lines of macros. Do not indent line wraps in the description.
```
# This is the description of the method. Line wraps in the description# must not be indented.## @return [ Symbol ] For macros, wraps must be double-space indented#   on the second, third (and so on) lines.
```
Whitespace: Do not use leading/trailing empty comment lines, or more than one consecutive empty comment line.
```
# DO THIS:# @return [ Symbol ] The return valuedef my_method
# NOT THIS:# @return [ Symbol ] The return value#def my_method
# NOT THIS:# @param [ Symbol ] foo The input value### @return [ Symbol ] The return valuedef my_method(foo)
```

Type Declaration

Type Unions: Use pipe | to denote a union of allowed types.
```
# @param [ Symbol | String ] name Either a Symbol or a String.
```
Nested Types: Use angle brackets < > to denote type nesting.
```
# @param [ Array<Symbol> ] array An Array of symbols.
```
Hash: Use comma , to denote the key and value types.
```
# @param [ Hash<Symbol, Integer> ] hash A Hash whose keys are Symbols,#   and whose values are Integers.
```
Array: Use pipe | to denote a union of allowed types.
```
# @param [ Array<Symbol | String> ] array An Array whose members must#   be either Symbols or Strings.
```
Array: Use comma , to denote the types of each position in a tuple.
```
# @return [ Array<Symbol, Integer, Integer> ] A 3-member Array whose first#   element is a Symbol, and whose second and third elements are Integers.
```
Array: Use pipe | on the top level if the inner types cannot be mixed within the Array.
```
# @param [ Array<Symbol> | Array<Hash> ] array An Array containing only#   Symbols, or an Array containing only Hashes. The Array may not contain#   a mix of Symbols and Hashes.
```
Nested Types: For clarity, use square brackets [ ] to denote nested unions when commas are also used.
```
# @param [ Hash<Symbol, [ true | false ]> ] hash A Hash whose keys are Symbols,#   and whose values are boolean values.
```
Ruby Values: Specific values may be denoted in the type using Ruby syntax.
```
# @param [ :before | :after ] timing One of the Symbol values :before or :after.
```
True, False, and Nil: Use true, false, and nil rather than TrueClass, FalseClass, and NilClass. Do not use Boolean as a type since it does not exist in Ruby.
```
# DO THIS:# @param [ true | false | nil ] bool A boolean or nil value.
# NOT THIS:# @param [ TrueClass | FalseClass | NilClass ] bool A boolean or nil value.# @param [ Boolean ] bool A boolean value.
```
Return Self: Specify return value self where a method returns self.
```
# @return [ self ] Returns the object itself.
```
Splat Args: Use three-dot ellipses ... in the type declaration and star * in the parameter name to denote a splat.
```
# @param [ String... ] *items The list of items' names as Strings.def buy_groceries(*items)
```
Splat Args: Do not use Array as the type unless each arg is actually an Array.
```
# DO NOT DO THIS:# @param [ Array<String> ] *items The list of items' names as Strings.def buy_groceries(*items)
buy_groceries("Cheese", "Crackers", "Wine")
# DO THIS:# @param [ Array<String>... ] *arrays One or more arrays containing name parts.def set_people_names(*arrays)
set_people_names(["Harlan", "Sanders"], ["Jane", "K", ""Doe"], ["Jim", "Beam"])
```
Splat Args: Use comma , to denote positionality in a splat.
```
# @param [ Symbol..., Hash ] *args A list of names, followed by a hash#   as the optional last arg.def say_hello(*args)
```
Splat Args: Specify type unions with square brackets [ ].
```
# @param [ [ String | Symbol ]... ] *fields A splat of mixed Symbols and Strings.
```
Keyword Arguments: Following YARD conventions, use @param for keyword arguments, and specify keyword argument names as symbols.
```
# @param [ String ] query The search string# @param [ Boolean ] :exact_match Whether to do an exact match# @param [ Integer ] :results_per_page Number of resultsdef search(query, exact_match: false, results_per_page: 10)
```
Hash Options: Define hash key-value options with @option macro immediately following the Hash @param. Note @option parameter names are symbols.
```
# @param opts [ Hash<Symbol, Object> ] The optional hash argument or arguments.# @option opts [ String | Array<String> ] :items The items as Strings to include.# @option opts [ Integer ] :limit An Integer denoting the limit.def buy_groceries(opts = {})
```
Double Splats: Use double-star ** in the parameter name to denote a keyword arg splat (double splat). Note that type does not need declared on the double-splat element, as it is implicitly <Symbol, Object>. Instead, define value types with @option macro below. Note @option parameter names are symbols.
```
# @param **kwargs The optional keyword argument or arguments.# @option **kwargs [ String | Array<String> ] :items The items as Strings to include.# @option **kwargs [ Integer ] :limit An Integer denoting the limit.def buy_groceries(**kwargs)
```
Blocks: Use @yield to specify when the method yields to a block.
```
# @yield [ Symbol, Symbol, Symbol ] Evaluate the guess of who did the crime.#   Must take the person, location, and weapon used. Must return true or false.def whodunit  yield(:mustard, :ballroom, :candlestick)end
```
Blocks: If the method explicitly specifies a block argument, specify the block argument using @param preceded by an ampersand &, and also specify @yield. Note @yield must be used even when method calls block.call rather than yield internally.
```
# @param &block The block.# @yield [ Symbol, Symbol, Symbol ] Evaluate the guess of who did the crime.#   Must take the person, location, and weapon used. Must return true or false.def whodunit(&block)  yield(:scarlet, :library, :rope)end
# @param &block The block.# @yield [ Symbol, Symbol, Symbol ] Evaluate the guess of who did the crime.#   Must take the person, location, and weapon used. Must return true or false.def whodunit(&block)  block.call(:plum, :kitchen, :pipe)end
```
Blocks: Use @yieldparam and @yieldreturn instead of @yield where beneficial for clarity.
```
# @param &block The block.# @yieldparam [ Symbol ] The person.# @yieldparam [ Symbol ] The location.# @yieldparam [ Symbol ] The weapon used.# @yieldreturn [ true | false ] Whether the guess is correct.def whodunit(&block)  yield(:peacock, :conservatory, :wrench)end
```
Proc Args: Use @param (not @yield) for proc arguments. The inputs to the proc may be specified as subtypes.
```
# @param [ Proc<Integer, Integer, Integer> ] my_proc Proc argument which must#   take 3 integers and must return true or false whether the guess is valid.def guess_three(my_proc)  my_proc.call(42, 7, 88)end
```

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