Add NamedTuple#reverse_merge (#16229)

Co-authored-by: stephann <[email protected]>

Author: andrykonchin

spec/std/named_tuple_spec.cr

@@ -503,6 +503,16 @@ describe "NamedTuple" do
     NamedTuple.new.merge(NamedTuple.new).should eq(NamedTuple.new)
   end
 
+  it "does reverse merge with other named tuple" do
+    a = {one: 1, two: 2, three: 3, four: 4, five: 5, "im \"string": "works"}
+    b = {two: "Two", three: true, "new one": "ok"}
+    a.reverse_merge(b).reverse_merge(four: "Four").reverse_merge(NamedTuple.new).should eq({one: 1, two: 2, three: 3, four: 4, five: 5, "new one": "ok", "im \"string": "works"})
+  end
+
+  it "does reverse merge two empty named tuples" do
+    NamedTuple.new.reverse_merge(NamedTuple.new).should eq(NamedTuple.new)
+  end
+
   it "does types" do
     tuple = {a: 1, b: 'a', c: "hello"}
     tuple.class.types.to_s.should eq("{a: Int32, b: Char, c: String}")

src/named_tuple.cr

@@ -340,6 +340,23 @@ struct NamedTuple
     {% end %}
   end
 
+  # Merges two named tuples into one, returning a new named tuple.
+  # If a key is defined in both tuples, the value and its type are used from **self** (original tuple)
+  #
+  # ```
+  # a = {foo: "Hello", bar: "Old"}
+  # b = {bar: "New", baz: "Bye"}
+  # a.reverse_merge(b) # => {foo: "Hello", bar: "Old", baz: "Bye"}
+  # ```
+  def reverse_merge(other : NamedTuple)
+    other.merge(**self)
+  end
+
+  # :ditto:
+  def reverse_merge(**other)
+    reverse_merge(other)
+  end
+
   # Returns a hash value based on this name tuple's size, keys and values.
   #
   # See also: `Object#hash`.