Render Ruby ERB templates, inline, with variables bound and available local variables in the template. ✨ This technique is useful for rendering test fixtures via ERB, for example.

erb_now.rb

require "ostruct"

# A wrapper around a single ERB template that will bind the given Hash of values,
# making them available as local variables w/in the template.
class ErbNow < OpenStruct
  # Render a given ERB +template+ string, binding the entries in the given +attrs+ Hash
  # as local variables in the template, with the key as the variable name.
  #
  # @example
  #
  # template = <<~ERB
  #  <h1>Hello, <%= name %>!</h1>
  #  <p>The current time is: <time datetime="<%= timestamp %>"><%= timestamp.strftime("%d of %B, %Y")%></time>.</p>
  # ERB
  #
  # ErbNow.render(template, name: "Alice", timestamp: Time.now)
  #
  # => <h1>Hello, Alice</h1>
  # => <p>The current time is: <time datetime="2020-12-16 10:31:36 -0500">16 of December, 2020</time>.</p>
  #
  # @param [String] template An ERB template, as a String.
  # @param [Hash] attrs A Hash of values to be bound to the template, with the key as the local name.
  def self.render(template, attrs = {})
    new(attrs).render(template)
  end

  def render(template)
    ERB.new(template).result(binding)
  end
end

This could be made more robust by accepting an IO-object, or a String-ish object as the template param. Something like

def render(template)
  template = template.read if template.respond_to?(:read)
  template = String(template)
  ERB.new(template).result(binding)
end

To date I've not needed this extra machinery, but please let me know if you do! I'm curious to know how others might use this technique.