https://github.com/egonSchiele/contracts.ruby/issues/300
https://github.com/egonSchiele/contracts.ruby/commit/88fd1d841615e59c873d7da64d050d3a251634dd

From 88fd1d841615e59c873d7da64d050d3a251634dd Mon Sep 17 00:00:00 2001
From: PikachuEXE <pikachuexe@gmail.com>
Date: Wed, 5 Oct 2022 10:27:41 +0800
Subject: [PATCH] * Update all references to Fixnum to Integer

Deprecated in ruby 2.4
--- a/lib/contracts/builtin_contracts.rb
+++ b/lib/contracts/builtin_contracts.rb
@@ -95,7 +95,7 @@ def self.[](*vals)
 
     # Takes a variable number of contracts.
     # The contract passes if any of the contracts pass.
-    # Example: <tt>Or[Fixnum, Float]</tt>
+    # Example: <tt>Or[Integer, Float]</tt>
     class Or < CallableClass
       def initialize(*vals)
         super()
@@ -120,7 +120,7 @@ def to_s
 
     # Takes a variable number of contracts.
     # The contract passes if exactly one of those contracts pass.
-    # Example: <tt>Xor[Fixnum, Float]</tt>
+    # Example: <tt>Xor[Integer, Float]</tt>
     class Xor < CallableClass
       def initialize(*vals)
         super()
@@ -146,7 +146,7 @@ def to_s
 
     # Takes a variable number of contracts.
     # The contract passes if all contracts pass.
-    # Example: <tt>And[Fixnum, Float]</tt>
+    # Example: <tt>And[Integer, Float]</tt>
     class And < CallableClass
       def initialize(*vals)
         super()
--- a/spec/builtin_contracts_spec.rb
+++ b/spec/builtin_contracts_spec.rb
@@ -30,7 +30,7 @@ def passes(&some)
   end
 
   describe "Num:" do
-    it "should pass for Fixnums" do
+    it "should pass for Integers" do
       passes { @o.double(2) }
     end
 
--- a/spec/fixtures/fixtures.rb
+++ b/spec/fixtures/fixtures.rb
@@ -100,11 +100,11 @@ def sum_three(vals)
     end
   end
 
-  Contract ({ :name => String, :age => Fixnum }) => nil
+  Contract ({ :name => String, :age => Integer }) => nil
   def person(data)
   end
 
-  Contract C::StrictHash[{ :name => String, :age => Fixnum }] => nil
+  Contract C::StrictHash[{ :name => String, :age => Integer }] => nil
   def strict_person(data)
   end
 
@@ -119,7 +119,7 @@ def hash_complex_contracts(data)
   def nested_hash_complex_contracts(data)
   end
 
-  Contract C::KeywordArgs[:name => String, :age => Fixnum] => nil
+  Contract C::KeywordArgs[:name => String, :age => Integer] => nil
   def person_keywordargs(name: "name", age: 10)
   end
 
@@ -529,30 +529,30 @@ def initialize(day, month)
     @month = month
   end
 
-  Contract C::None => Fixnum
+  Contract C::None => Integer
   def silly_next_day!
     self.day += 1
   end
 
-  Contract C::None => Fixnum
+  Contract C::None => Integer
   def silly_next_month!
     self.month += 1
   end
 
-  Contract C::None => Fixnum
+  Contract C::None => Integer
   def clever_next_day!
     return clever_next_month! if day == 31
     self.day += 1
   end
 
-  Contract C::None => Fixnum
+  Contract C::None => Integer
   def clever_next_month!
     return next_year! if month == 12
     self.month += 1
     self.day = 1
   end
 
-  Contract C::None => Fixnum
+  Contract C::None => Integer
   def next_year!
     self.month = 1
     self.day = 1
@@ -610,7 +610,7 @@ def on_response(status, body)
       body + "!"
     end
 
-    Contract Fixnum, String => String
+    Contract Integer, String => String
     def on_response(status, body)
       "error #{status}: #{body}"
     end