Merge pull request #15 from Kaligo/feature/guard-passing-constructor

Add ResultMonad::GuardClause#pass method which can be used to pass guards

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## 0.7.1
+
+### New features
+
+- Add `ResultMonad::GuardClause#pass` method which can be used to pass guards.
+
 ## 0.7.0
 
 ### New features

README.md

@@ -314,7 +314,7 @@ class Foo
 
   def call
     guard :bar_guard
-    guard { baz_guard }
+    qux = guard { baz_guard }
   end
 
   private
@@ -329,9 +329,9 @@ class Foo
 
   def baz_guard
     if qux?
-      error(errors: ["Qux failed."])
+      pass("Qux")
     else
-      success
+      error(errors: ["Qux failed."])
     end
   end
 end

lib/stimpack/result_monad/guard_clause.rb

@@ -2,6 +2,8 @@
 
 module Stimpack
   module ResultMonad
+    PassResult = Result.new(:klass, :errors, :_value, keyword_init: true)
+
     # This module adds a `#guard` method, which can be used inside a `#call`
     # to declare a step which, if it fails, breaks the flow of the method and
     # propagates the error result.
@@ -58,7 +60,13 @@ def guard(label = nil, &block)
 
         raise GuardFailed, result if result.failed?
 
-        result
+        result.unwrap!
+      end
+
+      # A standardized result object which can be used to pass guards.
+      #
+      def pass(value = nil)
+        PassResult.new(klass: self.class, errors: nil, _value: value)
       end
 
       def self.included(klass)

lib/stimpack/result_monad/result.rb

@@ -3,6 +3,8 @@
 module Stimpack
   module ResultMonad
     class Result < Struct
+      class UnwrapError < StandardError; end
+
       def successful?
         errors.nil?
       end
@@ -11,6 +13,13 @@ def failed?
         !successful?
       end
 
+      def unwrap!
+        raise UnwrapError, "Can not unwrap a failed result." if failed?
+        return if klass.blank_result?
+
+        public_send(result_key)
+      end
+
       def inspect
         if successful?
           "<#{klass}:successful #{result_key} : #{self[result_key].inspect}>"

lib/stimpack/version.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module Stimpack
-  VERSION = "0.7.0"
+  VERSION = "0.7.1"
 end

spec/stimpack/result_monad/guard_clause_spec.rb

@@ -27,9 +27,10 @@ def self.to_s
 
       def call
         guard :foo
-        guard { bar }
+        bar_result = guard { bar }
+        baz_result = guard { baz }
 
-        success(foo: "bar")
+        success(foo: bar_result + baz_result)
       end
 
       private
@@ -41,6 +42,10 @@ def foo
       def bar
         # Stubbed in test cases.
       end
+
+      def baz
+        pass("Baz")
+      end
     end
   end
 
@@ -56,7 +61,8 @@ def bar
     double(
       Stimpack::ResultMonad::Result,
       failed?: false,
-      errors: []
+      unwrap!: "Foo",
+      errors: nil
     )
   end
 
@@ -86,6 +92,7 @@ def bar
       end
 
       it { expect(instance.()).to be_successful }
+      it { expect(instance.().foo).to eq("FooBaz") }
     end
 
     context "when a guard fails" do

spec/stimpack/result_monad/result_spec.rb

@@ -36,4 +36,14 @@ def self.to_s
       it { expect(instance.error_result(errors: "Oops!").inspect).to eq("<Foo:failed errors : \"Oops!\">") }
     end
   end
+
+  describe "#unwrap!" do
+    context "when result is successful" do
+      it { expect(instance.success_result(foo: "bar").unwrap!).to eq("bar") }
+    end
+
+    context "when result is failed" do
+      it { expect { instance.error_result(errors: "Oops!").unwrap! }.to raise_error(described_class::UnwrapError) }
+    end
+  end
 end