‘Iacta alea est’
We proved that nested templates were possible by either instantiating multiple instances of a Hypertext::DSL class and combining them or by modifying the subclass to render layout, template and partial.
In this post I want to see what nested templates might look like when loading fragments from a file versus defining them in the DSL subclass.
As a reminder we are starting off with this code as the base:
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
For starters, let’s change the Context#initialize method to accept a string instead of a block. That way we can pass in the contents of a file.
class Context < Hypertext::DSL
- def initialize(params, &block)
+ def initialize(params, fragment)
params.each do |key, val|
instance_variable_set(sprintf("@%s", key), val)
end
- super(&block)
+ super(fragment)
end
end
And let’s test that out with a basic template:
Template.new({}, 'text "Hello, World"').to_s
Now Hypertext::DSL#initialize expects a block so that’s not going to cut the mustard. Let’s do some surgery to be able to continue down this path.
class Hypertext
class DSL
def initialize(string)
@ht = Hypertext.new
instance_eval <<-CODE
#{string}
CODE
end
end
end
Now that’s a little extreme, so rather than monkey patch the class, we can see that the only thing we need to do is to set the instance variable. Let’s do that in our Context class instead.
class Context < Hypertext::DSL
def initialize(params, fragment)
params.each do |key, val|
instance_variable_set(sprintf("@%s", key), val)
end
- super(fragment)
+ @ht = Hypertext.new
+ instance_eval fragment
end
end
Now, if we create a template using a string instead of a block we can check to see whether or not this works:
puts Template.new({}, 'text "Hello, World!"').to_s
# =>
# Hello, World!
Looking good. Let’s try with a template file as follows:
# index.ht
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
And loading that in:
params = { page_title: "Hello, World!" }
template = Template.new(params, File.read("index.ht"))
puts template.to_s
Gives us the following result:
# =>
# <html lang="en-GB">
# <head>
# <title>
# Hello, World!
# </title>
# </head>
# <body>
# <h1 id="id-15">
# Welcome
# </h1>
# </body>
# </html>
That’s looking good.
And that’s all I’ve got time for today. We’re reading the template in from a file and successfully executing it in the right context with both helper methods and variables. In a future post we can explore both layouts and partials loaded from file in a similar manner and how they fit together.
—Sunday 4th April 2021.