Struggle on define a variable in macro, use it outside where expanding it

Help & Support
1

I am struggle on migration one of our small go project to use kemal + avaram.

for avoid duplicate code, i try extract some common code (which in rails, we treat as before_action) into macro,
Maybe i do things wrong, it that is it, please point it out the correct way, anyway, let me show one example:

# define a macro here for used in several blocks
private macro get_user(env)
  open_id = env.params.url["open_id"]
  user = UserQuery.new.open_id(open_id).first    # <= i define a user variable in macro.

  if user.nil?
	env.response.status_code = 400
	next "Error"
  end
  {% debug %}
end

post path.admin_update_user do |env|
   get_user(env)                                   # <= use macro here, the user can be visited in ECR template.
   # ...
end

post path.admin_update_user do |env|
   get_user(env)                                   # <= use macro here too
   

   # i try to use `user` object here, but no luck.
   UpdateUser.update!(user, env.params)
end

As you can see, i get compile time error, like this:

Error: undefined method 'user' for top-level

If you declared 'user' in a suffix if, declare it in a regular if for this to work. 
If the variable was declared in a macro it's not visible outside it)

So, use user outside macro is not supported, right?

What is the correct way to do things like this? as you can see, what i want is just a
before_action like things, which can return early if user is nil.

Thank you.

2

I think the gist of the problem is the macro isn’t expanded yet when the compiler encounters the update method call.

Doing something like this seems to work:

get_user(env)
{% begin %}
  UpdateUser.update!(user, env.params)
{% end %}

Tho technically speaking using a macro in this context actually results in more code in the program. Could probably just use a method for this.

EDIT: A method might be a bit tricky with how kemal handles error handling. I.e. you need to exit early from the block, which you can’t do from outside of it…

EDIT2: You also dont really need to pass env to the macro, as you’re not using that parameter, nor would it work the way you’re thinking.

3

Yes, my fault, env is not necessary for this case

this seem like not work.

4

Macros can’t define local variables.

1 Like
5

It deff, does. I just tried it:

require "kemal"

class UserQuery
  def open_id(id)
    pp id
    [1, 2, 3]
  end
end

module UpdateUser
  def self.update!(u, params)
    pp u
  end
end

# define a macro here for used in several blocks
private macro get_user(env)
  open_id = env.params.url["open_id"]
  user = UserQuery.new.open_id(open_id).first    # <= i define a user variable in macro.

  if user.nil?
    env.response.status_code = 400
    next "Error"
  end
end

post "/bar/:open_id" do |env|
  get_user(env) # <= use macro here too
  {% begin %}
    # i try to use `user` object here, but no luck.
    UpdateUser.update!(user, env.params)
  {% end %}
end

Kemal.run
6

Oops, it my fault.

it not works for me because my code is included in a macro, like this:

module AdminUserController
  macro included
    # my code is here.
	macro get_user
      open_id = env.params.url["open_id"]
      user = UserQuery.new.open_id(open_id).first

	  if !user.nil?
		env.response.status_code = 400
		next "Error"
	  end

      user
    end
	
	get ... do
	  \{% begin %}
	    ...
	  \{% end }	
	end
  end
end

i have to escaped it to make it works.

7

Here’s an advice that will save you a lot of trouble: don’t use macros. You don’t need them. I’m sure of it. Please rewrite your code in a different way. For example get_user could return User or nil, and respond with an error in case of nil. Then you use it like this:

get_user(env) || next "Error"

I recommend not using macros at all in the beginning. Macros are mostly used for library code, not for application code.

5 Likes
8

Yes! i consider more deeper understood the macro … it not elixir