"desc 'description'" 抽成背后的魔力是什么？

Question

例如 https://github.com/locomotivecms/wagon/blob/master/Rakefile#L23

desc 'build the gem and release it to rubygems.org'
task release: :gem do
  sh "gem push pkg/locomotivecms_wagon-#{gemspec.version}.gem"
end

当我运行rake --task时，它作为描述返回。

rake clobber_package   # Remove package products
rake gem               # Build the gem file locomotivecms_wagon-2.2.0.beta1.gem
rake package           # Build all the packages
rake release           # build the gem and release it to rubygems.org
rake repackage         # Force a rebuild of the package files
rake spec              # Run RSpec code examples
rake spec:integration  # Run RSpec code examples
rake spec:unit         # Run RSpec code examples

但是我不明白他们怎么能接受描述，不是每次调用描述时都会替换它吗？他们如何知道特定描述属于特定任务？

Answer 1

想象一下简单的 DSL 有一个状态（非常天真的实现）：

@tasks = []
@current = nil

def desc text
  @current = Task.new(desc: text)
end

def task params, &cb
  @current.update(params)
  yield
   ....
  @tasks << @current
  @current = nil
end

上面的代码需要额外的检查等，但想法是：有状态 DSL 收集任务及其描述。

"desc 'description'" 抽成背后的魔力是什么？

What is the magic behind "desc 'description'" on rake?

ruby

rake