feat: add pattern matching by deconstruct

Author: initdc

.rubocop.yml

@@ -39,3 +39,6 @@ Layout/LineLength:
 
 Lint/UnusedBlockArgument:
   Enabled: false
+
+Style/ConditionalAssignment:
+  EnforcedStyle: assign_to_condition

lib/rs/option.rb

@@ -183,6 +183,10 @@ def ==(other)
     other.is_a?(Some) && @value == other.unwrap && @value_type == other.value_type
   end
 
+  def deconstruct
+    [self, @value]
+  end
+
   def initialize(value)
     if value == nil
       raise WrapNil.new("Cannot create Some[T](value) with nil")
@@ -208,6 +212,10 @@ def ==(other)
     other.is_a?(None) && @value_type == other.value_type
   end
 
+  def deconstruct
+    [self]
+  end
+
   def initialize(value_type = Class)
     if !value_type.is_a?(Class)
       raise TypeError.new(value_type)

lib/rs/result.rb

@@ -204,6 +204,10 @@ def ==(other)
     other.is_a?(Ok) && @value == other.unwrap && @value_type == other.value_type && @error_type == other.error_type
   end
 
+  def deconstruct
+    [self, @value]
+  end
+
   def initialize(value)
     if value == nil
       raise WrapNil.new("Cannot create Ok[T, E] with nil")
@@ -250,6 +254,10 @@ def ==(other)
     other.is_a?(Err) && @error == other.unwrap_err && @value_type == other.value_type && @error_type == other.error_type
   end
 
+  def deconstruct
+    [self, @error]
+  end
+
   def initialize(error)
     if error == nil
       raise WrapNil.new("Cannot create Err[T, E] with nil")

spec/rs/option_spec.rb

@@ -106,7 +106,7 @@
     expect(y.unwrap_or(0)).to eq 12
   end
 
-  it "pattern_matching" do
+  it "pattern matching" do
     def divide(numerator, denominator)
       if denominator == 0
         None[Float]
@@ -116,13 +116,35 @@ def divide(numerator, denominator)
     end
 
     result = divide(3.0, 1.0)
-    case result
-    when Some
-      x = result.unwrap
-    else
-      x = "Cannot divide by 0"
-    end
+    x = case result
+        when Some
+          result.unwrap
+        else
+          "Cannot divide by 0"
+        end
     expect(x).to eq 3.0
+
+    x = Some.new(2)
+    tx = case x
+         in Some, Integer => i
+           i
+         in Some, Float => f
+           f
+         in None
+           0
+         end
+
+    expect(tx).to eq 2
+
+    x = None.new
+    tx = case x
+         in Some, any
+           any
+         in None
+           0
+         end
+
+    expect(tx).to eq 0
   end
 
   it "type ==" do

spec/rs/result_spec.rb

@@ -19,6 +19,32 @@
     expect { Err.new(nil) }.to raise_error Rs::Result::WrapNil
   end
 
+  it "pattern matching" do
+    x = Ok[Float, String] { 2.0 }
+    tx = case x
+         in Ok, Integer => i
+           i
+         in Ok, Float => f
+           f
+         in Err, String => str
+           str
+         else
+           "mismatch"
+         end
+
+    expect(tx).to eq 2.0
+
+    x = Err[Float, String] { "foo" }
+    tx = case x
+         in Ok, any
+           any
+         in Err, str
+           str
+         end
+
+    expect(tx).to eq "foo"
+  end
+
   it "is_ok" do
     x = Ok.new(-3)
     expect(x.is_ok).to be true