Feature request: Pass array/Regexp to namespace/request methods

Currently, if I have 2 endpoints I want to merge into one, all I can do is to loop and create requests:

%w(a b c).each do |key|
  namespace key do
    get do
      "hello #{key}"
    end
  end
end

%w(e f g).each do |key|
  namespace key do
    get do
      "hello again #{key}"
    end
  end
end

In the case above, I can't use named namespace (namespace ":key") because it'll take over both request groups.

A nicer way would be to be able to send an array or regexp to namespace or get:

namespace %w(a b c) do
  get do
    "hello"
  end
end

namespace %r[^(?<key>e|f|g)$] do # regexp to support named groups
  get do
    "hello #{params[:key]}"
  end
end

get %r[^(?<key>h|i|j)$] do
  "hello #{params[:key]}"
end

Kind of aliasing same requests to a single block (also saves memory) for API changes, backward compatibility etc.

Start by tracing the namespace and get request-handling entry points in the Grape codebase, then review how route patterns and named parameters are currently processed. Done means arrays and regular expressions work with namespace and request methods, including the named-group examples in the issue, without requiring repeated blocks.