Add convenience method Dry::Configurable::Settings#replace

Gemfile

@@ -1,16 +1,16 @@
 # frozen_string_literal: true
 
-source 'https://rubygems.org'
+source "https://rubygems.org"
 
-eval_gemfile 'Gemfile.devtools'
+eval_gemfile "Gemfile.devtools"
 
 gemspec
 
 group :benchmarks do
-  gem 'benchmark-ips'
+  gem "benchmark-ips"
 end
 
 group :tools do
-  gem 'hotch'
-  gem 'pry-byebug', platform: :mri
+  gem "hotch"
+  gem "pry-byebug", platform: :mri
 end

Rakefile

@@ -1,8 +1,8 @@
 # frozen_string_literal: true
 
-require 'rspec/core/rake_task'
+require "rspec/core/rake_task"
 
-desc 'Run all specs in spec directory'
+desc "Run all specs in spec directory"
 RSpec::Core::RakeTask.new(:spec)
 
 task default: :spec

bin/console

@@ -1,13 +1,13 @@
 #!/usr/bin/env ruby
 # frozen_string_literal: true
 
-require 'bundler/setup'
-require 'dry/configurable'
+require "bundler/setup"
+require "dry/configurable"
 
 begin
-  require 'pry-byebug'
+  require "pry-byebug"
   Pry.start
 rescue LoadError
-  require 'irb'
+  require "irb"
   IRB.start
 end

lib/dry/configurable/setting.rb

@@ -69,6 +69,11 @@ def initialize(name, input: Undefined, default: Undefined, **options)
         evaluate if input_defined?
       end
 
+      def merge(setting)
+        input.merge(setting.input) if input_defined?
+        evaluate
+      end
+
       # @api private
       def input_defined?
         !input.equal?(Undefined)

lib/dry/configurable/settings.rb

@@ -23,6 +23,35 @@ def initialize(elements = EMPTY_ARRAY)
         initialize_elements(elements)
       end
 
+      def replace(settings)
+        unless settings.is_a? Dry::Configurable::Settings
+          raise ArgumentError, "settings must be a Dry::Configurable::Settings"
+        end
+
+        settings.each do |setting|
+          self << setting
+        end
+      end
+
+      def merge(settings)
+        unless settings.is_a? Dry::Configurable::Settings
+          raise ArgumentError, "settings must be a Dry::Configurable::Settings"
+        end
+
+        settings.each do |setting|
+          merge_setting(setting)
+        end
+      end
+
+      # @api private
+      def merge_setting(setting)
+        if key?(setting.name)
+          elements[setting.name].merge(setting)
+        else
+          self << setting
+        end
+      end
+
       # @api private
       def <<(setting)
         elements[setting.name] = setting

spec/integration/dry/configurable/setting_spec.rb

@@ -185,6 +185,68 @@
 
     include_context "configurable behavior"
 
+    context "can be configured with another class's settings" do
+      let(:other_klass) do
+        Class.new do
+          extend Dry::Configurable
+        end
+      end
+
+      it "should deep merge" do
+        klass.setting :database do
+          setting :type, "postgresql"
+          setting :host, "remote"
+          setting :port, 12_345
+          setting :deep do
+            setting :one, 1
+            setting :two, 2
+          end
+        end
+
+        other_klass.setting :database do
+          setting :host, "localhost"
+          setting :port
+          setting :deep, 3
+        end
+
+        other_klass._settings.merge(klass._settings.dup)
+        expect(other_klass.config.database.host).to eql("localhost")
+        expect(other_klass.config.database.port).to eql(nil)
+        expect(other_klass.config.database.type).to eql("postgresql")
+        expect(other_klass.config.database.deep).to eql(3)
+      end
+
+      it "replaces with each" do
+        klass.setting :hello, "world"
+        klass._settings.each do |setting|
+          other_klass._settings << setting.dup
+        end
+        expect(other_klass.config.hello).to eql("world")
+      end
+
+      it "replaces with replace" do
+        klass.setting :hello, "world"
+        other_klass._settings.replace(klass._settings.dup)
+        expect(other_klass.config.hello).to eql("world")
+      end
+
+      it "deep replace" do
+        klass.setting :database do
+          setting :dsn, "localhost"
+        end
+
+        other_klass._settings.replace(klass._settings.dup)
+        expect(other_klass.config.database.dsn).to eql("localhost")
+      end
+
+      it "throws an error if the settings aren't Dry::Configurable::Settings" do
+        klass.setting :hello, "world"
+        expect { other_klass._settings.replace(klass) }.to raise_error do |error|
+          expect(error.class).to be(ArgumentError)
+        end
+      end
+    end
+
     context "with a subclass" do
       let(:subclass) do
         Class.new(klass)