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Coding Style Guide

This document describes the coding style used in this project. It also serves as an incubator for the coding style guide used throughout the Asciidoctor project. Note that these guidelines are still evolving.

The coding style rules are as follows:

  • Indent using 2 spaces, generally.

  • Indent successive lines of conditions, method arguments or ternary expressions using 4 spaces (but not data structures or chained method calls).

  • Don’t indent when lines in a case block.

  • Wrap API docs at 120 characters.

  • Leave a single space inside brackets of a Hash (let it breathe).

    { "key" => "value" }
  • Use JSON-style key-value pair when key is a Symbol.

    { key: "value" }
  • Fully qualify the class name (beginning with ::) of any type not in the current namespace.

    ::File.extname path
  • Use triple equals to check for type, placing the type on the left hand side.

    ::Hash === attrs
  • Drop parentheses around method arguments of a method definition.

    def integrate document, collection_name = nil
      ...
    end
  • Drop parentheses around method arguments of an isolated method call.

    source = ::File.expand_path config['source']
    if key.start_with? '!'
      ...
    end
  • Don’t surround expression value of variable assignment in parantheses.

    part = section.sectname == 'part'
    subs = format_mark == '`' ? BASIC_SUBS : NORMAL_SUBS
  • Drop parentheses when using fallback values for assignments.

    a, b = $1 || $3, $2 || $4
  • When brackets are required for a method call, use lisp-style brackets

    (::File.dirname docfile)
  • For chained method calls, wrap parentheses around nested method call. (NOTE: This produces a warning in Ruby < 2).

    asciidoctor_config.replace (Utils.symbolize_keys asciidoctor_config)
  • Add %r prefix to inline regexp when used as the first argument of a method.

    files.grep %r/^spec\//
  • Use parentheses outside of a method call when parentheses are required.

    layout = collection_name ? (collection_name.chomp 's') : 'page'
    if (::Jekyll::Utils.method dlg_method.name).arity == -1
      ...
    end
  • Use parentheses where required, such as around the accumulator seed value for a collection predicate.

    hash.each_with_object({}) {|(key, val), accum| accum[key.to_sym] = val }
  • Don’t put curly braces around entries in an options Hash (i.e., symbol keys).

    record_path_info document, source_only: true
  • Use a trailing condition for single-line statements.

    clear_path_info if Document === document
  • Put parentheses around a variable assignment inside a condition.

    if (imagesdir = attrs['imagesdir'])
  • Use variable reference to check for nil.

    if base
  • Use %() instead of double quotes around interpolated strings.

    %(--- #{val})
  • Use single quotes around string if interpolation is not required.

    'asciidoctor'
  • Name constants using pascal style.

    NewLine = %(\n)
  • Define each static regular expression (regexp) as a constant so it’s precompiled. Append Rx suffix to name.

    ExtensionRx = /^\.adoc$/
  • Place the regular expression (regexp) before the string when creating a match.

    ExtensionRx =~ ext
    ExtensionRx.match ext
  • Use parentheses in traditional style when writing test assertions.

    expect(site.config['asciidoc']['processor']).to eql('asciidoctor')
    expect(result.key? 'icons').to be true
    expect(contents).to match('<div class="page-content">')
  • Use .size to get the length of a collection and .length to get the length of a string.

    "abc".length
    [1, 2, 3].size
  • Use #[0] and #[-1] to get the first and last element of an Array, respectively, rather than #first and #last. NOTE: You still have to use #first and #last on an Enumerable object that’s not an Array.

    a = [1, 2, 3]
    a[0]
    a[-1]
  • Pass symbol reference to .map when invoking no-args method on iteration variable (parens are required).

    lines.map(&:strip)
  • When calling raise to raise an exception, pass the exception class as the first argument and the message as the second. Write the message as a sentence, but exclude the period.

    raise ::ArgumentError, 'Not a valid argument'
  • Use name instead of symbol to alias a method.

    alias copy original
  • When only one private method, add keyword to method definition; otherwise use block form

  • Use do…​end for multi-line blocks and { …​ } for single-line blocks (even when chained)

  • Use {}.tap {|accum| arr.each {|v| accum[v] = v } } to create a Hash from an Array or Hash

  • Use default_ as prefix instead of suffix

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