Roxygen Guide

Documentation Style Guide

This style guide describes how to properly document R6 class generators.

Sections

Note that section names must always end with a :, otherwise they will not be rendered.

@section Construction:

Describes how to instantiate the class. To mimick R's "Usage", this section should start with a code block (three backticks) where an exemplary assignment to some variable with a short name is done:

x = MyClass$new(id, type = NULL)

In the following, refer to the instance as x, e.g. x$type.

Below this block, document each argument, see below for format.

@section Fields:

Describes member variables and active bindings.

@section Methods:

Describes public methods and class methods ($new).

@section Param Set:

Describes parameters in $param_set / $param_vals. Format is the same as for "Public Members / Active Bindings".

Style guide for entities:

• slot description in @section Construction, in @section Fields and @section Param Set: name in backticks, followed by :: (with spaces; possibly multiple spaces for vertical alignment), followed by type description, followed by \cr.

  `id` :: `character(1)` \cr

  `output` :: [data.table] with columns "name", "train", "predict" \cr

• method description in @section Methods: function's formals in backticks, with default values if applicable, followed by \cr. Class methods (usually Class$new) prepended with class name and dollar sign.

  `Graph$new()` \cr

  `add_edge(src_id, dst_id, src_channel = NULL, dst_channel = NULL)` \cr

• method type description in @section Methods: classes in backticks (linked if not default R package classes; possibly with length given in parentheses if vector type), alternative classes separated by vertical bars (|), different arguments comma-separated, all surrounded by parentheses. Spaces before and after |, after ,, but not after ( or before ) or ,. Followed by arrow (-> with spaces), followed by return type, followed by \cr. Functions without input ("nullary functions") have () in-type, functions with invisible(NULL) (e.g. print, plot) have `NULL` return type.

  () -> `NULL` \cr

  (`character(1)` | `NULL`, `character`, named `list`) -> [`data.table`] with columns `id`, `state` \cr

• R6, S3 class names: Backtick-quoted, possibly linked if mentioned for the first time or in a member var type description / function type description, but not linked if in base R or in an R default package.

  Many [`Graph`]s

  The `Graph`'s size

  This is a [`data.table`], not a `data.frame`

• member variable / AB slot names: Backtick-quoted. Prepended by dollar sign except in their description line in @section Public Members / Active Bindings.

  The `Graph`'s `$id`

• method names: Backtick-quoted. Prepended by dollar sign, followed by (), exception is their description line in @section Methods.

  Use `$add_pipeop()` to...

• self when referring to return value of a mutator: Backtick quoted. Otherwise use the class name instead.

  (`character()`) -> `self`

  The `Graph`'s `$id` , not `self$id`

• any when referring to any possible type: Backtick quoted.

  `any`

• literal strings: Backtick and double quoted:

  The default ID is `"pca"`

• column names of data.tables / data.frames: Backtick quoted, comma separated, without "and" if in a member var type description / function type description.

  `output` :: `data.table` with columns `name`, `train`, `predict` \cr

  The table's `name` column contains...

• functions that are not R6 class methods: Followed by (), and in brackets ([]).

  Use [print()] to..., but Use `$add_pipeop()` to...

The following should not be backtick-quoted:

• 'named' in named `list()` and similar
• parentheses, vertical bars, arrows, equal signs in function type description

The following should be linked (i.e. put in []):

• Every function that is not an R6 method.
• First mention of any type / class that is not in R default packages (The "first mention" can be an occurrence in a type description; if the class is mentioned later it shouldn't be linked any more).
• Every type, class, function that is not in R default packages in a member var type description or function type description.

Don't link things like "character(1)" or "character()" because (1) it would be silly and (2) it would lead to an inconsistent typeface.

Linking

• Simple links: [link].
• Links of things in monospace typeface: [`link`] exception for functions, they appear in monospace automatically: [link()].
• Linking to entities in other packages: [`package::link`] or [package::link()]. If the package should not be part of the text: [`link`][package::link] or [link()][package::link].
• Linking to other packages themselves: [mlr3][mlr3::mlr3-package]

@family

The @family tag creates a group of documentation pages that mutually link each other. Writing @family <TEXT> will create the line "Other <TEXT>: [link] [link] [link]". The following rules for this:

• Family <TEXT> should be short but is allowed to, and should probably, contain spaces. It should make a natural sentence when written as "Other <TEXT>:". This means if it is a noun (e.g. "PipeOps") it should therefore probably be plural.
• A page can be member of multiple families if that is natural.
• Do not create families with only one member.

@include

It is a good idea to @include the file defining the the superclass, if any.

Example

Syntax

• <>: object dependent strings.
• {{}}: optional strings
• {{|}}: alterantives

#' @title <classname>
#'
#' @usage NULL
#' @format {{[`R6Class`] object|Abstract [`R6Class`]}}{{ inheriting from [`<superclass>`]}}.
#' {{@include <superclass>.R}}
#'
#' @description
#' Long form description. Mentions [`PipeOp`] once. Mentions `PipeOp` twice.
#'
#' Another paragraph in long form description.
#'
#' @section Construction:
#' ```
#' cl = <classname>$new(x, y)
#' ```
#' * `x` :: `character`\cr
#'   Some variable `x`, may be `NULL`.
#' * `y` :: `numeric(1)`\cr
#'   Some numeric variable `y`.
#'
#' @section Fields:
#' * `<varname>`    :: named `list` of [`Graph`] \cr
#'   Description of `$<varname>`. Mentions `Graph`, but doesn't link it, because
#'   this is not the first mention of `Graph`.
#' * `<varname2>`   :: `any` \cr
#'   Description of `$<varname2>`. Notice how a dollar-sign is used when referring
#'   to slots.
#'
#' @section Methods:
#' * `mutate(x = default)` \cr
#'   (`any`) -> `self` \cr
#'   When referring to `$mutate()` and other methods, always use the dollar sign
#'   and an empty pair of parentheses.
#' * `produce()` \cr
#'   () -> [`PipeOp`] \cr
#'   Description of `$produce()` function.
#'
#' @family mlr3pipelines backend related
#' @export
#' @examples
#' g = Graph$new()