Expressions

[bkeepers]

Described by @jnunemaker in #557, Expressions are a new syntax for defining rules in Flipper and will enable much more sophisticated feature flipping. We're going to try to get this merged into Flipper as an experimental new feature while we put the finishing touches on it.

[jhubert]

So excited for this! Game changer 🎉

[swishstache]

When an expression match requires a method call (such as "user.admin?") should we expect to just add additional values to "flipper_properties"?

  def flipper_properties
    super.merge!("is_admin" => admin?)
  end

[bkeepers]

@swishstache Yep, that's what we were thinking. Does that work for you?

[swishstache]

@swishstache Yep, that's what we were thinking. Does that work for you?

It does! 🎉👍

[swishstache]

When using multiple actors, how might we achieve a match for a combination of them? For example, enabling a feature for "basic plan" user actors but, only for those that belong to a specific organization actor.

Example Code (based on the code from "examples/expressions.rb")

org_foo = Org.new(1, {
  "type" => "Org",
  "id" => 1,
  "now" => NOW,
})

org_bar = Org.new(33, {
  "type" => "Org",
  "id" => 33,
  "now" => NOW,
})

user_ted = User.new(1, {
  "type" => "User",
  "id" => 1,
  "plan" => "basic",
  "age" => 39,
  "team_user" => true,
  "now" => NOW,
})

user_lasso = User.new(32, {
  "type" => "User",
  "id" => 32,
  "plan" => "basic",
  "age" => 39,
  "team_user" => true,
  "now" => NOW,
})

# Basic plan users under Foo org only
is_foo_org = Flipper.property(:type).eq("Org"), Flipper.property(:flipper_id).eq("Org;1")
is_basic_plan_user = Flipper.property(:type).eq("User"), Flipper.property(:plan).eq("basic")

Flipper.enable :neat_feature, Flipper.all(is_foo_org, is_basic_plan_user)

# A basic plan user under Foo organization
assert Flipper.enabled?(:neat_feature, [org_foo, user_ted]) # => Expected true but was false. Please correct.

# A basic plan user under Bar organization
refute Flipper.enabled?(:neat_feature, [org_bar, user_lasso]) # => false

[jnunemaker]

@swishstache I'd collapse the actors into the properties. For expressions, the goal would be to pass all the context in one actor and then let the expression sort it out. For example, instead of passing org and user, I'd pass the user with the current org in the properties.

Forgive any typos or slight incorrectness in the pseudo-code below...

class OrgUser
  include Flipper::Actor

  def initialize(org, user)
    @user = user
    @org = org
  end

  def flipper_id
    "User;#{@user.id};Org;#{@org.id}" # or it could be @user.flipper_id or whatever makes sense
  end

  def flipper_properties
    @user.flipper_properties.merge("org_id" => @org.id)
  end
end

org_foo = Org.new(1, {
  "type" => "Org",
  "id" => 1,
  "now" => NOW,
})

org_bar = Org.new(33, {
  "type" => "Org",
  "id" => 33,
  "now" => NOW,
})

user_ted = User.new(1, {
  "type" => "User",
  "id" => 1,
  "plan" => "basic",
  "age" => 39,
  "team_user" => true,
  "now" => NOW,
  "org_id" => 1,
})

user_lasso = User.new(32, {
  "type" => "User",
  "id" => 32,
  "plan" => "basic",
  "age" => 39,
  "team_user" => true,
  "now" => NOW,
  "org_id" => 33,
})

# Basic plan users under Foo org only
is_foo_org = Flipper.property(:org_id).eq(1)
is_basic_plan_user = Flipper.all(Flipper.property(:type).eq("User"), Flipper.property(:plan).eq("basic"))

Flipper.enable :neat_feature, Flipper.all(is_foo_org, is_basic_plan_user)

# A basic plan user under Foo organization
assert Flipper.enabled?(:neat_feature, OrgUser.new(org_foo, user_ted)) # => true

# A basic plan user under Bar organization
refute Flipper.enabled?(:neat_feature, OrgUser.new(org_bar, user_lasso)) # => false

@bkeepers has been knee deep in this so he may have better ideas, but I was picturing something like that.

The only other thing I can think of is to merge all properties into one big hash but then you have to deal with collisions of property keys which seems painful.

[bkeepers]

I'm going to work on getting this released this week as "alpha", so I'm going to go ahead and merge this and I'll track any further work in #557.