Insert into erb binding

ruby-talk
1

I have a class that takes a template, parses it through ERB, then takes the output for some custom manipulation. When the class is created as an object a binding is passed to it to be passed to the template. Is it possible to get the class to insert a variable into the binding? Example:

Template:
<xml><%=@variable1%> <%=variable2%></xml>

class:
class Renderer
    def initialize(template_file, apply_binding)
       @file = template_file
       @binding = apply_binding
    end

    def render
       @variable2 = "There"

       template = ERB.new(File.read(@file))
       template_results = template.result(@binding)

       # Perform on template results
    end
end

Program:
@variable1 = "Hello"
renderer = Renderer.new('template.xml', binding)
renderer.render

current output: <xml>Hello</xml>
desired output: <xml>Hello There</xml>

So I want the renderer class to add @variable2 to the binding before calling the template.

···

--

*Jeremy Wells*

2

IIRC this is (more or less) from Rails code:

        def evaluate_locals(local_assigns = {})
                b = binding
                local_assigns.each { |key, value| eval "#{key} =
local_assigns[\"#{key}\"]", b }
                b
        end

The trick is to use eval with binding as an additional argument.

···

On 12/7/06, Jeremy Wells <jwells@servalsystems.co.uk> wrote:

I have a class that takes a template, parses it through ERB, then takes
the output for some custom manipulation. When the class is created as an
object a binding is passed to it to be passed to the template. Is it
possible to get the class to insert a variable into the binding? Example:

Template:
<xml><%=@variable1%> <%=variable2%></xml>

class:
class Renderer
    def initialize(template_file, apply_binding)
       @file = template_file
       @binding = apply_binding
    end

    def render
       @variable2 = "There"

       template = ERB.new(File.read(@file))
       template_results = template.result(@binding)

       # Perform on template results
    end
end

Program:
@variable1 = "Hello"
renderer = Renderer.new('template.xml', binding)
renderer.render

current output: <xml>Hello</xml>
desired output: <xml>Hello There</xml>

So I want the renderer class to add @variable2 to the binding before
calling the template.

3

surely this won't work as the binding in my case is coming from an external source, so the ruby in the eval won't have access to the variable in the render method?

Jan Svitok wrote:

···

On 12/7/06, Jeremy Wells <jwells@servalsystems.co.uk> wrote:

I have a class that takes a template, parses it through ERB, then takes
the output for some custom manipulation. When the class is created as an
object a binding is passed to it to be passed to the template. Is it
possible to get the class to insert a variable into the binding? Example:

Template:
<xml><%=@variable1%> <%=variable2%></xml>

class:
class Renderer
    def initialize(template_file, apply_binding)
       @file = template_file
       @binding = apply_binding
    end

    def render
       @variable2 = "There"

       template = ERB.new(File.read(@file))
       template_results = template.result(@binding)

       # Perform on template results
    end
end

Program:
@variable1 = "Hello"
renderer = Renderer.new('template.xml', binding)
renderer.render

current output: <xml>Hello</xml>
desired output: <xml>Hello There</xml>

So I want the renderer class to add @variable2 to the binding before
calling the template.

IIRC this is (more or less) from Rails code:

       def evaluate_locals(local_assigns = {})
               b = binding
               local_assigns.each { |key, value| eval "#{key} =
local_assigns[\"#{key}\"]", b }
               b
       end

The trick is to use eval with binding as an additional argument.

--

*Jeremy Wells*
Serval Systems Ltd.

www.servalsystems.co.uk <http://www.servalsystems.co.uk>
Tel: 01342 331940
Fax: 01342 331950

4

So once more: The trick is to use eval with binding as an additional argument.
That means when eval gets a binding as the second argument, it will operate
in that context. In this case, if you eval("@var = 123",
some_binding), the variable @var will be set in that binding.

Beware that you are modifying the original binding, so you might
corrupt the original caller.
Maybe @binding = apply_binding.dup will be neccessary.

(I added @ in the template - it was missing)

require 'erb'

# TEMPLATE = "<xml><%=@variable1%> <%=variable2%></xml>"
TEMPLATE = "<xml><%=@variable1%> <%=@variable2%></xml>"

class Renderer
    def initialize(template_file, apply_binding)
       @file = template_file
       @binding = apply_binding
    end

    def render
        # @variable2 = "There"
        eval("@variable2 = \"There\"", @binding)

        # template = ERB.new(File.read(@file))
        template = ERB.new(TEMPLATE)

        template_results = template.result(@binding)

        # Perform on template results

  template_results
    end
end

require 'test/unit'

class TestERB < Test::Unit::TestCase
  def test_variable
    @variable1 = "Hello"

    renderer = Renderer.new('template.xml', binding)
    assert_equal "<xml>Hello There</xml>", renderer.render
  end

end

···

On 12/8/06, Jeremy Wells <jwells@servalsystems.co.uk> wrote:

surely this won't work as the binding in my case is coming from an
external source, so the ruby in the eval won't have access to the
variable in the render method?

5

Ah ok, I get it but here is the problem, which I didn't specify... @variable2 doesn't hold static data, it holds an object, which is created in the render method like so:

def render
    @variable2 = Object.new
    eval("@variable2 = ???", @binding)

That's what I meant by the variable not being in the binding, thus not accessible to eval.

Jan Svitok wrote:

···

On 12/8/06, Jeremy Wells <jwells@servalsystems.co.uk> wrote:

surely this won't work as the binding in my case is coming from an
external source, so the ruby in the eval won't have access to the
variable in the render method?

So once more: The trick is to use eval with binding as an additional argument.
That means when eval gets a binding as the second argument, it will operate
in that context. In this case, if you eval("@var = 123",
some_binding), the variable @var will be set in that binding.

Beware that you are modifying the original binding, so you might
corrupt the original caller.
Maybe @binding = apply_binding.dup will be neccessary.

(I added @ in the template - it was missing)

require 'erb'

# TEMPLATE = "<xml><%=@variable1%> <%=variable2%></xml>"
TEMPLATE = "<xml><%=@variable1%> <%=@variable2%></xml>"

class Renderer
   def initialize(template_file, apply_binding)
      @file = template_file
      @binding = apply_binding
   end

   def render
       # @variable2 = "There"
       eval("@variable2 = \"There\"", @binding)

       # template = ERB.new(File.read(@file))
       template = ERB.new(TEMPLATE)

       template_results = template.result(@binding)

       # Perform on template results

    template_results
   end
end

require 'test/unit'

class TestERB < Test::Unit::TestCase
    def test_variable
        @variable1 = "Hello"

        renderer = Renderer.new('template.xml', binding)
        assert_equal "<xml>Hello There</xml>", renderer.render
    end

end

--

*Jeremy Wells*
Serval Systems Ltd.

www.servalsystems.co.uk <http://www.servalsystems.co.uk>
Tel: 01342 331940
Fax: 01342 331950