Allow block with Hash#delete

spec/std/hash_spec.cr

@@ -257,6 +257,15 @@ describe "Hash" do
       a = {1 => 2}
       a.delete(2).should be_nil
     end
+
+    describe "with block" do
+      it "executes block if key is not found" do
+        found = true
+        a = {1 => 2}
+        a.delete(3) { found = false }
+        found.should be_false
+      end
+    end
   end
 
   describe "size" do

src/hash.cr

@@ -198,7 +198,23 @@ class Hash(K, V)
     yield value
   end
 
-  # Deletes the key-value pair and returns the value.
+  # Deletes the key-value pair and returns the value, else yields *key* with given block.
+  #
+  # ```
+  # h = {"foo" => "bar"}
+  # h.delete("foo") { |key| "#{key} not found" } # => "bar"
+  # h.fetch("foo", nil)                          # => nil
+  # h.delete("baz") { |key| "#{key} not found" } # => "baz not found"
+  # ```
+  def delete(key, &block)
+    if val = delete(key)
+      val
+    else
+      yield key
+    end
+  end
+
+  # Deletes the key-value pair and returns the value, otherwise returns `nil`.
   #
   # ```
   # h = {"foo" => "bar"}