‘Iacta alea est’
At the end of a previous post applying the Markaby variables and helpers API to Hypertext I asked the question:
Are there other, simpler, easier, more fitting APIs? Is there a way to accomplish the delegation of unknown methods to the helper without method_missing?
What I love about doing a lot of this API exploration out in the open is that releasing an imperfect solution into the world does at least two things: it frees up your mind to move beyond the point at which you currently stand; and it invites others into the process, often involving minds much smarter and more experienced than my own.
That latter scenario was the case today when I received a Gist from Mr. Martens showcasing a blindly obvious way to introducing variables and helpers into Hypertext without at all modifying the Hypertext::DSL class. Sometimes you’re so busy looking for something that you don’t realise it’s staring you right in the face.
Rather than complicated instance variable partitioning, or relying on meta-programming ‘magic’ we can use one of the tried and trusted tools of Ruby’s object oriented heritage, inheritance.
That is, we can create a context object by inheriting from the Hypertext::DSL class:
class Context < Hypertext::DSL
end
Instead of patching the Hypertext::DSL#initialize method, we can simply extend it in the sub class and introduce the variable assignment identically to how we have been doing it from the start, using instance_variable_set.
class Context < Hypertext::DSL
def initialize(params, &block)
params.each do |key, val|
instance_variable_set(sprintf("@%s", key), val)
end
super(&block)
end
end
If we want helper methods, then we can define them in this context class:
class Context < Hypertext::DSL
…
def id_generator
"id-#{rand(100)}"
end
end
or we can give birth to a ‘grandchild’:
class Template < Context
def id_generator
"id-#{rand(100)}"
end
end
If we use this last approach, then a full example would look similar to the following:
require "hypertext"
require "hypertext/dsl"
class Context < Hypertext::DSL
def initialize(params, &block)
params.each do |key, val|
instance_variable_set(sprintf("@%s", key), val)
end
super(&block)
end
end
class Template < Context
def id_generator
"id-#{rand(100)}"
end
end
html = Template.new page_title: "Hello, World!" do
html lang: "en-GB" do
head do
title do
text @page_title
end
end
body do
h1 id: id_generator do
text "Welcome"
end
end
end
end
puts html.to_s
# =>
# <html lang="en-GB">
# <head>
# <title>
# Hello, World!
# </title>
# </head>
# <body>
# <h1 id="id-60">
# Welcome
# </h1>
# </body>
# </html>
No magic. No complications. Just straightforward inheritance. So simple and obvious it never even occurred to me.
Thank you, Mr. Martens, for opening my eyes. Again.
—Wednesday 31st March 2021.