This is an example of some _really_ simple templating in Crystal that leverages method calls which are dispatched dynamically to get the data to fill out the template.

gistfile1.txt

require "./src/send"

struct Template
  getter body : String

  def initialize(@body)
  end

  def transform(data)
    @body.gsub(/(###([_\w]+)###)/) do |match|
      data.send($2)
    end
  end
end

class DataThing
  include Send
  getter name : String
  
  def initialize(@name)
  end

  def class_name
    self.class.name
  end

  def current_time
    Time.local
  end
end

Send.activate

t = Template.new("I am a template rendered for ###name### and I get my data from an object of type ###class_name###. Oh, and the time is ###current_time###.")

data = DataThing.new("Kirk")

puts t.transform(data)

gistfile2.txt

> crystal run template.cr
I am a template rendered for Kirk and I get my data from an object of type DataThing. Oh, and the time is 2021-06-15 14:44:34 -06:00.