Implement Hash#{<,<=,>,>=} operators for sub/superset checking

spec/std/hash_spec.cr

@@ -88,6 +88,46 @@ describe "Hash" do
     end
   end
 
+  describe "<" do
+    it do
+      h1 = {"a" => 1, "b" => 2}
+      h2 = {"a" => 1, "b" => 2, "c" => 3}
+      (h1 < h2).should be_true
+      (h2 < h1).should be_false
+      (h1 < h1).should be_false
+    end
+  end
+
+  describe "<=" do
+    it do
+      h1 = {"a" => 1, "b" => 2}
+      h2 = {"a" => 1, "b" => 2, "c" => 3}
+      (h1 <= h2).should be_true
+      (h2 <= h1).should be_false
+      (h1 <= h1).should be_true
+    end
+  end
+
+  describe ">" do
+    it do
+      h1 = {"a" => 1, "b" => 2}
+      h2 = {"a" => 1, "b" => 2, "c" => 3}
+      (h1 > h2).should be_false
+      (h2 > h1).should be_true
+      (h1 > h1).should be_false
+    end
+  end
+
+  describe ">=" do
+    it do
+      h1 = {"a" => 1, "b" => 2}
+      h2 = {"a" => 1, "b" => 2, "c" => 3}
+      (h1 >= h2).should be_false
+      (h2 >= h1).should be_true
+      (h1 >= h1).should be_true
+    end
+  end
+
   describe "[]" do
     it "gets" do
       a = {1 => 2}

src/hash.cr

@@ -882,6 +882,29 @@ class Hash(K, V)
     true
   end
 
+  # Returns `true` if `self` is subset of *other*.
+  def <(other : Hash)
+    return false if self == other
+    self <= other
+  end
+
+  # Returns `true` if `self` is subset of *other* or equals to *other*.
+  def <=(other : Hash)
+    all? do |key, value|
+      other[key]? == value
+    end
+  end
+
+  # Returns `true` if *other* is subset of `self`.
+  def >(other : Hash)
+    other < self
+  end
+
+  # Returns `true` if *other* is subset of `self` or equals to `self`.
+  def >=(other : Hash)
+    other <= self
+  end
+
   # See `Object#hash(hasher)`
   def hash(hasher)
     # The hash value must be the same regardless of the