1. Using shorthand syntax: #

This:

<% @inbox.messages.each do |message| %>
  <%= render partial: 'messages/message', locals: { message: message } %>
<% end %>

Equals this:

<%= render @inbox.messages %>

2. Less magic = More control! # 

<%= render @messages %>
<%= render partial: "messages/message", collection: @messages, locals: { a: "b" } %>

<%= render @message %>
<%= render partial: "messages/message", locals: { message: @message, a: "b" } %>

3. Passing ONLY locals to a partial: #

  • Does not work:
<%= render "layouts/foo", locals: { a: "b" } %>
  • works:
<%= render partial: "layouts/foo", locals: { a: "b" } %>
  • also works:
<%= render "layouts/foo", a: "b" %>

4. Check if a local variable is present # 

local_assigns[:a].present?
# => true
local_assigns[:a].presence
# => "b"
local_assigns[:a]
# => "b"

Found this ^ one here

Resources: