Jay Fields' Thoughts

Update at bottom

By default Rake Tasks append behavior every time they are defined. The following example shows that both definitions are executed.

require 'rubygems'
require 'rake'

task :the_task do
  p "one"
end

task :the_task do
  p "two"
end

Rake::Task[:the_task].invoke 
# >> "one"
# >> "two"

I like this behavior, but sometimes you want to overwrite a task instead of appending to what's already there.

When you no longer want the existing behavior the overwrite method can come in handy.

require 'rubygems'
require 'rake'

class Rake::Task
  def overwrite(&block)
    @actions.clear
    enhance(&block)
  end
end

task :the_task do
  p "one"
end

Rake::Task[:the_task].overwrite do
  p "two"
end


Rake::Task[:the_task].invoke 
# >> "two"

The overwrite method is good, but sometimes you want to redefine the task using one of the specialized Rake tasks. I recently wanted to redefine the test task, so I created the abandon method to remove the existing definition.

require 'rubygems'
require 'rake'
require 'rake/testtask'

class Rake::Task
  def abandon
    @actions.clear
  end
end

task :the_task do
  p "one"
end

Rake::Task[:the_task].abandon

Rake::TestTask.new(:the_task) do |t|
  t.libs << "test"
  t.pattern = 'test/**/*_test.rb'
  t.verbose = true
end

Rake::Task[:the_task].invoke
# >> Expectations ..................
# >> Finished in 0.00442 seconds
# >> 
# >> Success: 18 fulfilled

Hopefully you wont need this type of thing very often, but it can be handy when you want to overwrite a task that has been previously by a framework you've included.

Update below...
Ola Bini pointed out that I'm not clearing the prerequisites. Clearing the prerequisites is something you can do without any modifications to rake.

Rake::Task[:task_name].prerequisites.clear

Also, if you want prerequisites cleared as part of overwrite or abandon, you can easily add it to both tasks.

class Rake::Task
  def overwrite(&block)
    @actions.clear
    prerequisites.clear
    enhance(&block)
  end
  def abandon
    prerequisites.clear
    @actions.clear
  end
end

Labels: rake