Question

I’m trying to use the Thor::Actions template method to generate some C++ test file templates, but erb keeps telling me that I have undefined variables and methods.

Here’s the calling code:

def test (name, dir)
  template "tasks/templates/new_test_file", "src/#{dir}/test/#{name}Test.cpp"
  insert_into_file "src/#{dir}/test/CMakeLists.txt", 
       "#{dir}/test/#{name}Test ", :after => "set(Local "
end

Here’s the template:

<% test_name = name + "Test" %>
#include <gtest/gtest.h>
#include "<%= dir %>/<%= name %>.h"

class <%= test_name %> : public testing::Test {
protected:
    <%= test_name %> () {}
    ~<%= test_name %> () {}
    virtual void SetUp () {}
    virtual void TearDown () {}
};

// Don't forget to write your tests before you write your implementation!
TEST_F (<%= test_name %>, Sample) {
   ASSERT_EQ(1 + 1, 3);
}

What do I have to do to get name and dir into scope here? I have more complex templates that I need this functionality for too.

Answer 1

ERB uses ruby’s binding object to retrieve the variables that you want. Every object in ruby has a binding, but access to the binding is limited to the object itself, by default. you can work around this, and pass the binding that you wish into your ERB template, by creating a module that exposes an object’s binding, like this:

module GetBinding
  def get_binding
    binding
  end
end

Then you need to extend any object that has the vars you want with this module.

something.extend GetBinding

and pass the binding of that object into erb

something.extend GetBinding
some_binding = something.get_binding

erb = ERB.new template
output = erb.result(some_binding)

for a complete example of working with ERB, see this wiki page for one of my projects: https://github.com/derickbailey/Albacore/wiki/Custom-Tasks