Added readme and a few more tests

Author: joelmoss

README.md

@@ -0,0 +1,18 @@
+# Delivered: Simple runtime type checking for Ruby method signatures
+
+Delivered gives you the ability to define method signatures in Ruby, and have them checked at
+runtime. This is useful for ensuring that your methods are being called with the correct arguments,
+and for providing better error messages when they are not.
+
+Simply define a method signature using the `sig` method directly before the method to be checked,
+and Delivered will check that the method is being called with the correct arguments and types. it
+can alos chreck the return value of the method.
+
+```ruby
+class User
+  sig String, age: Integer, returns: String
+  def create(name, age:)
+    "User #{name} created with age #{age}"
+  end
+end
+```

lib/delivered/signature.rb

@@ -2,7 +2,9 @@
 
 module Delivered
   module Signature
-    def sig(*sig_args, returns: nil, **sig_kwargs) # rubocop:disable Lint/UnusedMethodArgument
+    NULL = Object.new
+
+    def sig(*sig_args, returns: NULL, **sig_kwargs)
       meta = class << self; self; end
       meta.send :define_method, :method_added do |name|
         meta.send :remove_method, :method_added
@@ -17,11 +19,15 @@ def sig(*sig_args, returns: nil, **sig_kwargs) # rubocop:disable Lint/UnusedMeth
             value => ^(sig_kwargs[key])
           end
 
-          if block
-            send(:"__#{name}", *args, **kwargs, &block).tap { |x| x => returns }
-          else
-            send(:"__#{name}", *args, **kwargs).tap { |x| x => returns }
-          end
+          result = if block
+                     send(:"__#{name}", *args, **kwargs, &block)
+                   else
+                     send(:"__#{name}", *args, **kwargs)
+                   end
+
+          result => ^returns if returns != NULL
+
+          result
         end
       end
     end

test/delivered/signature.rb

@@ -6,7 +6,7 @@ class User
 
     attr_reader :town, :blk
 
-    sig String, Integer, town: String, returns: User
+    sig String, Integer, town: String
     def initialize(name, age = nil, town: nil, &block)
       @name = name
       @age = age
@@ -16,17 +16,41 @@ def initialize(name, age = nil, town: nil, &block)
 
     sig returns: String
     def to_s = "#{@name}, #{@age}"
+
+    sig returns: Integer
+    def age = @age.to_s
+
+    sig Integer, returns: Integer
+    attr_writer :age
   end
 
   it 'supports positional args' do
-    expect(User.new('Joel', 47).to_s).to be == 'Joel, 47'
+    user = User.new('Joel', 47)
+    expect(user.to_s).to be == 'Joel, 47'
   end
 
+  # it 'supports optional positional args'
+
   it 'supports block' do
     user = User.new('Joel', 47) { 'Hello' }
     expect(user.blk.call).to be == 'Hello'
   end
 
+  it 'checks return type' do
+    user = User.new('Joel', 47)
+    expect(user.to_s).to be == 'Joel, 47'
+  end
+
+  it 'raises on incorrect return type' do
+    user = User.new('Joel', 47)
+    expect { user.age }.to raise_exception NoMatchingPatternError
+  end
+
+  it 'checks return type with args' do
+    user = User.new('Joel', 47)
+    expect(user.age = 48).to be == 48
+  end
+
   it 'raises on missing args' do
     expect { User.new }.to raise_exception NoMatchingPatternError
   end