#なぜするのか
使っているライブラリやフレームワークのドキュメントを読んでも処理内容がよくわからなかったり、なんか怪しいと思った場合、どこにあるかわからない情報を探すより、確実に実行されるものを見た方が早い(一般的な話、なおWETなコードは除きます)事が多々有ります。
特にテストコードや、メタメタしてるコードを読むのは非常に勉強になります。
#Action View
RailsでWebアプリケーションを作るなら、ほぼ100%使うであろうrenderメソッドのコード根幹となる処理分岐は実はこんなに少ないコードで実装してあります。実際のrenderロジックは、他のクラスに集約して、自由に付け替え可能となるように実装されています。それぞれのクラスにrenderメソッドを実行させていることがわかります。
これらのクラスはabstructパターンで作られています。
#abstract_renderrer.rb
module ActionView
# This class defines the interface for a renderer. Each class that
# subclasses +AbstractRenderer+ is used by the base +Renderer+ class to
# render a specific type of object.
#
# The base +Renderer+ class uses its +render+ method to delegate to the
# renderers. These currently consist of
#
# PartialRenderer - Used for rendering partials
# TemplateRenderer - Used for rendering other types of templates
# StreamingTemplateRenderer - Used for streaming
#
# Whenever the +render+ method is called on the base +Renderer+ class, a new
# renderer object of the correct type is created, and the +render+ method on
# that new object is called in turn. This abstracts the setup and rendering
# into a separate classes for partials and templates.
class AbstractRenderer #:nodoc:
delegate :find_template, :find_file, :template_exists?, :any_templates?, :with_fallbacks, :with_layout_format, :formats, :to => :@lookup_context
def initialize(lookup_context)
@lookup_context = lookup_context
end
def render
raise NotImplementedError
end
protected
def extract_details(options)
@lookup_context.registered_details.each_with_object({}) do |key, details|
value = options[key]
details[key] = Array(value) if value
end
end
def instrument(name, **options)
options[:identifier] ||= (@template && @template.identifier) || @path
ActiveSupport::Notifications.instrument("render_#{name}.action_view", options) do |payload|
yield payload
end
end
def prepend_formats(formats)
formats = Array(formats)
return if formats.empty? || @lookup_context.html_fallback_for_js
@lookup_context.formats = formats | @lookup_context.formats
end
end
end
ここで delegateという予約メソッドがありますね。
これは、delegeteを実行した時点でそのクラスに実装されていないメソッドやプロパティなどを、toでシンボルで指定した先の変数に実装を任せて、とりあえずそのクラスのインスタンスからdelegateに指定された名前でメソッドの呼び出しをできるようにします。
このメソッドが呼び出された時に、toで指定された変数内に格納されたオブジェクトが,delegateされたメソッドを実装していた場合、delegete元のクラスのインスタンスからそのメソッドを渡す事ができます。例えば以下のようになります。
class A
def self.test
"Hello"
end
end
class B
delegate :test,to: :A
end
B.new.test => "Hello"
以上のようにBクラスのインスタンスからAクラスのクラスメソッドが呼べたのが分かると思います。当然この時,Aクラスのクラスメソッドにtestが定義されていなければ、実行時にエラーになります。私はrubyではこのようにして、抽象化するということはこのコードから学びました。
次に、yieldを見てみましょう。yieldはpythonでもC#でもよく使うので、イテレータとして順番に値を返すのだろうと思いきや、rubyは仕様がちょっと違うんですよね。
rubyのyieldは関数自体の戻り値として値をイテレートするわけではなく、yieldした変数を、渡されたブロックにインジェクトして、ブロックの呼び出し自体を繰り返します。分かりやすい例でいうと
python
def my_iter():
yield 1
yield 2
yield 3
it = my_iter()
for x in it:
print(x)
Ruby
def my_iter
yield 1
yield 2
yield 3
end
my_iter{|it|
puts it
}
以上のようにpythonのyieldは値を順番に返していくのに対し、rubyのyieldは呼ばれたタイミングでそのブロックにyieldした値をインジェクトしています。ただ、以下は全く無意味なコードですが
def for_each(list)
list.each do|n|
yield n
end
end
for_each([1,2,3]){|it|
puts it
}
とすると、メモリの動きまで調べたことないので、部処理までが一緒かどうかは分かりませんが、書き方が違うだけで本質的には同様な処理を実装できることが分かるのではないでしょうか。(ただrubyのyieldは中断と再開処理ができない？知ってる方いらっしゃれば教えて下さい。)
railsではpayloadの分だけ外部に処理を投げているようです。
そしておそらく、皆さんがrails開発をしていて一番気になるのが、optionはどれだけあるのか、どういう形式でデータを突っ込めるかだと思うのですが、例えばpartial_renderer.rbを例にして見てみます。
require "concurrent/map"
require "action_view/renderer/partial_renderer/collection_caching"
module ActionView
class PartialIteration
# The number of iterations that will be done by the partial.
attr_reader :size
# The current iteration of the partial.
attr_reader :index
def initialize(size)
@size = size
@index = 0
end
# Check if this is the first iteration of the partial.
def first?
index == 0
end
# Check if this is the last iteration of the partial.
def last?
index == size - 1
end
def iterate! # :nodoc:
@index += 1
end
end
# = Action View Partials
#
# There's also a convenience method for rendering sub templates within the current controller that depends on a
# single object (we call this kind of sub templates for partials). It relies on the fact that partials should
# follow the naming convention of being prefixed with an underscore -- as to separate them from regular
# templates that could be rendered on their own.
#
# In a template for Advertiser#account:
#
# <%= render partial: "account" %>
#
# This would render "advertiser/_account.html.erb".
#
# In another template for Advertiser#buy, we could have:
#
# <%= render partial: "account", locals: { account: @buyer } %>
#
# <% @advertisements.each do |ad| %>
# <%= render partial: "ad", locals: { ad: ad } %>
# <% end %>
#
# This would first render "advertiser/_account.html.erb" with @buyer passed in as the local variable +account+, then
# render "advertiser/_ad.html.erb" and pass the local variable +ad+ to the template for display.
#
# == The :as and :object options
#
# By default <tt>ActionView::PartialRenderer</tt> doesn't have any local variables.
# The <tt>:object</tt> option can be used to pass an object to the partial. For instance:
#
# <%= render partial: "account", object: @buyer %>
#
# would provide the <tt>@buyer</tt> object to the partial, available under the local variable +account+ and is
# equivalent to:
#
# <%= render partial: "account", locals: { account: @buyer } %>
#
# With the <tt>:as</tt> option we can specify a different name for said local variable. For example, if we
# wanted it to be +user+ instead of +account+ we'd do:
#
# <%= render partial: "account", object: @buyer, as: 'user' %>
#
# This is equivalent to
#
# <%= render partial: "account", locals: { user: @buyer } %>
#
# == \Rendering a collection of partials
#
# The example of partial use describes a familiar pattern where a template needs to iterate over an array and
# render a sub template for each of the elements. This pattern has been implemented as a single method that
# accepts an array and renders a partial by the same name as the elements contained within. So the three-lined
# example in "Using partials" can be rewritten with a single line:
#
# <%= render partial: "ad", collection: @advertisements %>
#
# This will render "advertiser/_ad.html.erb" and pass the local variable +ad+ to the template for display. An
# iteration object will automatically be made available to the template with a name of the form
# +partial_name_iteration+. The iteration object has knowledge about which index the current object has in
# the collection and the total size of the collection. The iteration object also has two convenience methods,
# +first?+ and +last?+. In the case of the example above, the template would be fed +ad_iteration+.
# For backwards compatibility the +partial_name_counter+ is still present and is mapped to the iteration's
# +index+ method.
#
# The <tt>:as</tt> option may be used when rendering partials.
#
# You can specify a partial to be rendered between elements via the <tt>:spacer_template</tt> option.
# The following example will render <tt>advertiser/_ad_divider.html.erb</tt> between each ad partial:
#
# <%= render partial: "ad", collection: @advertisements, spacer_template: "ad_divider" %>
#
# If the given <tt>:collection</tt> is +nil+ or empty, <tt>render</tt> will return nil. This will allow you
# to specify a text which will displayed instead by using this form:
#
# <%= render(partial: "ad", collection: @advertisements) || "There's no ad to be displayed" %>
#
# NOTE: Due to backwards compatibility concerns, the collection can't be one of hashes. Normally you'd also
# just keep domain objects, like Active Records, in there.
#
# == \Rendering shared partials
#
# Two controllers can share a set of partials and render them like this:
#
# <%= render partial: "advertisement/ad", locals: { ad: @advertisement } %>
#
# This will render the partial "advertisement/_ad.html.erb" regardless of which controller this is being called from.
#
# == \Rendering objects that respond to `to_partial_path`
#
# Instead of explicitly naming the location of a partial, you can also let PartialRenderer do the work
# and pick the proper path by checking `to_partial_path` method.
#
# # @account.to_partial_path returns 'accounts/account', so it can be used to replace:
# # <%= render partial: "accounts/account", locals: { account: @account} %>
# <%= render partial: @account %>
#
# # @posts is an array of Post instances, so every post record returns 'posts/post' on `to_partial_path`,
# # that's why we can replace:
# # <%= render partial: "posts/post", collection: @posts %>
# <%= render partial: @posts %>
#
# == \Rendering the default case
#
# If you're not going to be using any of the options like collections or layouts, you can also use the short-hand
# defaults of render to render partials. Examples:
#
# # Instead of <%= render partial: "account" %>
# <%= render "account" %>
#
# # Instead of <%= render partial: "account", locals: { account: @buyer } %>
# <%= render "account", account: @buyer %>
#
# # @account.to_partial_path returns 'accounts/account', so it can be used to replace:
# # <%= render partial: "accounts/account", locals: { account: @account} %>
# <%= render @account %>
#
# # @posts is an array of Post instances, so every post record returns 'posts/post' on `to_partial_path`,
# # that's why we can replace:
# # <%= render partial: "posts/post", collection: @posts %>
# <%= render @posts %>
#
# == \Rendering partials with layouts
#
# Partials can have their own layouts applied to them. These layouts are different than the ones that are
# specified globally for the entire action, but they work in a similar fashion. Imagine a list with two types
# of users:
#
# <%# app/views/users/index.html.erb %>
# Here's the administrator:
# <%= render partial: "user", layout: "administrator", locals: { user: administrator } %>
#
# Here's the editor:
# <%= render partial: "user", layout: "editor", locals: { user: editor } %>
#
# <%# app/views/users/_user.html.erb %>
# Name: <%= user.name %>
#
# <%# app/views/users/_administrator.html.erb %>
# <div id="administrator">
# Budget: $<%= user.budget %>
# <%= yield %>
# </div>
#
# <%# app/views/users/_editor.html.erb %>
# <div id="editor">
# Deadline: <%= user.deadline %>
# <%= yield %>
# </div>
#
# ...this will return:
#
# Here's the administrator:
# <div id="administrator">
# Budget: $<%= user.budget %>
# Name: <%= user.name %>
# </div>
#
# Here's the editor:
# <div id="editor">
# Deadline: <%= user.deadline %>
# Name: <%= user.name %>
# </div>
#
# If a collection is given, the layout will be rendered once for each item in
# the collection. For example, these two snippets have the same output:
#
# <%# app/views/users/_user.html.erb %>
# Name: <%= user.name %>
#
# <%# app/views/users/index.html.erb %>
# <%# This does not use layouts %>
# <ul>
# <% users.each do |user| -%>
# <li>
# <%= render partial: "user", locals: { user: user } %>
# </li>
# <% end -%>
# </ul>
#
# <%# app/views/users/_li_layout.html.erb %>
# <li>
# <%= yield %>
# </li>
#
# <%# app/views/users/index.html.erb %>
# <ul>
# <%= render partial: "user", layout: "li_layout", collection: users %>
# </ul>
#
# Given two users whose names are Alice and Bob, these snippets return:
#
# <ul>
# <li>
# Name: Alice
# </li>
# <li>
# Name: Bob
# </li>
# </ul>
#
# The current object being rendered, as well as the object_counter, will be
# available as local variables inside the layout template under the same names
# as available in the partial.
#
# You can also apply a layout to a block within any template:
#
# <%# app/views/users/_chief.html.erb %>
# <%= render(layout: "administrator", locals: { user: chief }) do %>
# Title: <%= chief.title %>
# <% end %>
#
# ...this will return:
#
# <div id="administrator">
# Budget: $<%= user.budget %>
# Title: <%= chief.name %>
# </div>
#
# As you can see, the <tt>:locals</tt> hash is shared between both the partial and its layout.
#
# If you pass arguments to "yield" then this will be passed to the block. One way to use this is to pass
# an array to layout and treat it as an enumerable.
#
# <%# app/views/users/_user.html.erb %>
# <div class="user">
# Budget: $<%= user.budget %>
# <%= yield user %>
# </div>
#
# <%# app/views/users/index.html.erb %>
# <%= render layout: @users do |user| %>
# Title: <%= user.title %>
# <% end %>
#
# This will render the layout for each user and yield to the block, passing the user, each time.
#
# You can also yield multiple times in one layout and use block arguments to differentiate the sections.
#
# <%# app/views/users/_user.html.erb %>
# <div class="user">
# <%= yield user, :header %>
# Budget: $<%= user.budget %>
# <%= yield user, :footer %>
# </div>
#
# <%# app/views/users/index.html.erb %>
# <%= render layout: @users do |user, section| %>
# <%- case section when :header -%>
# Title: <%= user.title %>
# <%- when :footer -%>
# Deadline: <%= user.deadline %>
# <%- end -%>
# <% end %>
class PartialRenderer < AbstractRenderer
include CollectionCaching
PREFIXED_PARTIAL_NAMES = Concurrent::Map.new do |h, k|
h[k] = Concurrent::Map.new
end
def initialize(*)
super
@context_prefix = @lookup_context.prefixes.first
end
def render(context, options, block)
setup(context, options, block)
@template = find_partial
@lookup_context.rendered_format ||= begin
if @template && @template.formats.present?
@template.formats.first
else
formats.first
end
end
if @collection
render_collection
else
render_partial
end
end
private
def render_collection
instrument(:collection, count: @collection.size) do |payload|
return nil if @collection.blank?
if @options.key?(:spacer_template)
spacer = find_template(@options[:spacer_template], @locals.keys).render(@view, @locals)
end
cache_collection_render(payload) do
@template ? collection_with_template : collection_without_template
end.join(spacer).html_safe
end
end
def render_partial
instrument(:partial) do |payload|
view, locals, block = @view, @locals, @block
object, as = @object, @variable
if !block && (layout = @options[:layout])
layout = find_template(layout.to_s, @template_keys)
end
object = locals[as] if object.nil? # Respect object when object is false
locals[as] = object if @has_object
content = @template.render(view, locals) do |*name|
view._layout_for(*name, &block)
end
content = layout.render(view, locals) { content } if layout
payload[:cache_hit] = view.cache_hit
content
end
end
# Sets up instance variables needed for rendering a partial. This method
# finds the options and details and extracts them. The method also contains
# logic that handles the type of object passed in as the partial.
#
# If +options[:partial]+ is a string, then the +@path+ instance variable is
# set to that string. Otherwise, the +options[:partial]+ object must
# respond to +to_partial_path+ in order to setup the path.
def setup(context, options, block)
@view = context
@options = options
@block = block
@locals = options[:locals] || {}
@details = extract_details(options)
prepend_formats(options[:formats])
partial = options[:partial]
if String === partial
@has_object = options.key?(:object)
@object = options[:object]
@collection = collection_from_options
@path = partial
else
@has_object = true
@object = partial
@collection = collection_from_object || collection_from_options
if @collection
paths = @collection_data = @collection.map { |o| partial_path(o) }
@path = paths.uniq.one? ? paths.first : nil
else
@path = partial_path
end
end
if as = options[:as]
raise_invalid_option_as(as) unless /\A[a-z_]\w*\z/.match?(as.to_s)
as = as.to_sym
end
if @path
@variable, @variable_counter, @variable_iteration = retrieve_variable(@path, as)
@template_keys = retrieve_template_keys
else
paths.map! { |path| retrieve_variable(path, as).unshift(path) }
end
self
end
def collection_from_options
if @options.key?(:collection)
collection = @options[:collection]
collection ? collection.to_a : []
end
end
def collection_from_object
@object.to_ary if @object.respond_to?(:to_ary)
end
def find_partial
find_template(@path, @template_keys) if @path
end
def find_template(path, locals)
prefixes = path.include?(?/) ? [] : @lookup_context.prefixes
@lookup_context.find_template(path, prefixes, true, locals, @details)
end
def collection_with_template
view, locals, template = @view, @locals, @template
as, counter, iteration = @variable, @variable_counter, @variable_iteration
if layout = @options[:layout]
layout = find_template(layout, @template_keys)
end
partial_iteration = PartialIteration.new(@collection.size)
locals[iteration] = partial_iteration
@collection.map do |object|
locals[as] = object
locals[counter] = partial_iteration.index
content = template.render(view, locals)
content = layout.render(view, locals) { content } if layout
partial_iteration.iterate!
content
end
end
def collection_without_template
view, locals, collection_data = @view, @locals, @collection_data
cache = {}
keys = @locals.keys
partial_iteration = PartialIteration.new(@collection.size)
@collection.map do |object|
index = partial_iteration.index
path, as, counter, iteration = collection_data[index]
locals[as] = object
locals[counter] = index
locals[iteration] = partial_iteration
template = (cache[path] ||= find_template(path, keys + [as, counter]))
content = template.render(view, locals)
partial_iteration.iterate!
content
end
end
# Obtains the path to where the object's partial is located. If the object
# responds to +to_partial_path+, then +to_partial_path+ will be called and
# will provide the path. If the object does not respond to +to_partial_path+,
# then an +ArgumentError+ is raised.
#
# If +prefix_partial_path_with_controller_namespace+ is true, then this
# method will prefix the partial paths with a namespace.
def partial_path(object = @object)
object = object.to_model if object.respond_to?(:to_model)
path = if object.respond_to?(:to_partial_path)
object.to_partial_path
else
raise ArgumentError.new("'#{object.inspect}' is not an ActiveModel-compatible object. It must implement :to_partial_path.")
end
if @view.prefix_partial_path_with_controller_namespace
prefixed_partial_names[path] ||= merge_prefix_into_object_path(@context_prefix, path.dup)
else
path
end
end
def prefixed_partial_names
@prefixed_partial_names ||= PREFIXED_PARTIAL_NAMES[@context_prefix]
end
def merge_prefix_into_object_path(prefix, object_path)
if prefix.include?(?/) && object_path.include?(?/)
prefixes = []
prefix_array = File.dirname(prefix).split("/")
object_path_array = object_path.split("/")[0..-3] # skip model dir & partial
prefix_array.each_with_index do |dir, index|
break if dir == object_path_array[index]
prefixes << dir
end
(prefixes << object_path).join("/")
else
object_path
end
end
def retrieve_template_keys
keys = @locals.keys
keys << @variable if @has_object || @collection
if @collection
keys << @variable_counter
keys << @variable_iteration
end
keys
end
def retrieve_variable(path, as)
variable = as || begin
base = path[-1] == "/".freeze ? "".freeze : File.basename(path)
raise_invalid_identifier(path) unless base =~ /\A_?(.*?)(?:\.\w+)*\z/
$1.to_sym
end
if @collection
variable_counter = :"#{variable}_counter"
variable_iteration = :"#{variable}_iteration"
end
[variable, variable_counter, variable_iteration]
end
IDENTIFIER_ERROR_MESSAGE = "The partial name (%s) is not a valid Ruby identifier; " +
"make sure your partial name starts with underscore."
OPTION_AS_ERROR_MESSAGE = "The value (%s) of the option `as` is not a valid Ruby identifier; " +
"make sure it starts with lowercase letter, " +
"and is followed by any combination of letters, numbers and underscores."
def raise_invalid_identifier(path)
raise ArgumentError.new(IDENTIFIER_ERROR_MESSAGE % (path))
end
def raise_invalid_option_as(as)
raise ArgumentError.new(OPTION_AS_ERROR_MESSAGE % (as))
end
end
end
実は、コミッターの方はすごく丁寧に実装にコメントを残してくれてることが多いので、ここで知らなかったことが解ることが多いです。ここでoptionsで検索かけてみると、partialだけでもオプションたくさんあることが解るのではないでしょうか。localeとかはよく使いますが、あまり馴染みのないものもありますね。delegateされたメソッドもちゃんと定義されています。
#masterブランチに追加されているTagHelperなるヘルパー
Railsの公式リリースの最新バージョンは5.0.0(と思いきや公式リポジトリでも5.0.1rc1,5.0.1rc2がつい三日ほど前にリリースされていました。)ですが、最新版のmasterブランチにはタグヘルパーなるヘルパーにチェーンメソッドが追加されています。
tag_helper.rb
これは、例えば、
<%= tag.h1 タイトル%>
<%# =><h1>タイトル</h1> %>
のようにchainでタグを追加していける機能のようですが、便利そうなので早くリリースされて欲しいですね。
#まとめ
ドキュメントやネットで情報探せば早く解決することもありますが、実際のコードの知見やそこで使われてるテクニックが見れてとてもいいですよ。また、難しそうな実装に見えて以外と簡単だったり、プロジェクトによっては、コードが綺麗に見えてぐちゃぐちゃだったりといろんな発見があると思います。技術力の伸び悩みを感じたらオープンソースでこの処理いいなと思うプロジェクトの真似をしてみるのがいいのではないでしょうかというお話でした。