ERB::Compiler

Compiles ERB templates into Ruby code; the compiled code produces the template result when evaluated. ERB::Compiler provides hooks to define how generated output is handled.

Internally ERB does something like this to generate the code returned by ERB#src:

compiler = ERB::Compiler.new('<>')
compiler.pre_cmd    = ["_erbout=+''"]
compiler.put_cmd    = "_erbout.<<"
compiler.insert_cmd = "_erbout.<<"
compiler.post_cmd   = ["_erbout"]

code, enc = compiler.compile("Got <%= obj %>!\n")
puts code

Generates:

#coding:UTF-8
_erbout=+''; _erbout.<< "Got ".freeze; _erbout.<<(( obj ).to_s); _erbout.<< "!\n".freeze; _erbout

By default the output is sent to the print method. For example:

compiler = ERB::Compiler.new('<>')
code, enc = compiler.compile("Got <%= obj %>!\n")
puts code

Generates:

#coding:UTF-8
print "Got ".freeze; print(( obj ).to_s); print "!\n".freeze

Evaluation

The compiled code can be used in any context where the names in the code correctly resolve. Using the last example, each of these print ‘Got It!’

Evaluate using a variable:

obj = 'It'
eval code

Evaluate using an input:

mod = Module.new
mod.module_eval %{
  def get(obj)
    #{code}
  end
}
extend mod
get('It')

Evaluate using an accessor:

klass = Class.new Object
klass.class_eval %{
  attr_accessor :obj
  def initialize(obj)
    @obj = obj
  end
  def get_it
    #{code}
  end
}
klass.new('It').get_it

Good! See also ERB#def_method, ERB#def_module, and ERB#def_class.