From a92700e93b9692f8c61f15a360d16baea9569c76 Mon Sep 17 00:00:00 2001
From: Delyan Angelov <delian66@gmail.com>
Date: Mon, 6 Nov 2023 20:09:05 +0200
Subject: [PATCH] maps: add maps.merge/2 and maps.merge_in_place/2 generic
 utility functions (#19776)

---
 vlib/maps/maps.v      | 22 +++++++++++
 vlib/maps/maps_test.v | 88 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 110 insertions(+)

diff --git a/vlib/maps/maps.v b/vlib/maps/maps.v
index a923fd6ddd..f28804acea 100644
--- a/vlib/maps/maps.v
+++ b/vlib/maps/maps.v
@@ -68,3 +68,25 @@ pub fn from_array[T](array []T) map[int]T {
 
 	return mp
 }
+
+// merge_in_place merges all elements of `m2` into the mutable map `m1`.
+// If a key exists in both maps, the value from `m1` will be overwritten by the
+// value from `m2`.
+// Note that this function modifes `m1`, while `m2` will not be.
+pub fn merge_in_place[K, V](mut m1 map[K]V, m2 map[K]V) {
+	for k, v in m2 {
+		m1[k] = v
+	}
+}
+
+// merge produces a map, that is the result of merging the first map `m1`,
+// with the second map `m2`. If a key exists in both maps, the value from m2,
+// will override the value from m1.
+// The original maps `m1` and `m2`, will not be modified. The return value is a new map.
+pub fn merge[K, V](m1 map[K]V, m2 map[K]V) map[K]V {
+	mut res := m1.clone()
+	for k, v in m2 {
+		res[k] = v
+	}
+	return res
+}
diff --git a/vlib/maps/maps_test.v b/vlib/maps/maps_test.v
index 88a673a5b5..11df779f02 100644
--- a/vlib/maps/maps_test.v
+++ b/vlib/maps/maps_test.v
@@ -107,3 +107,91 @@ fn test_from_array() {
 		5: 'f'
 	}
 }
+
+fn test_merge_in_place() {
+	mut m1 := {
+		'abc': 'def'
+		'aa':  'bb'
+	}
+	m2 := {
+		'xyz': 'zyx'
+		'aa':  'dd'
+	}
+	merge_in_place(mut m1, m2)
+	assert m1 == {
+		'abc': 'def'
+		'aa':  'dd'
+		'xyz': 'zyx'
+	}
+	assert m2 == {
+		'xyz': 'zyx'
+		'aa':  'dd'
+	}
+	//
+	mut im1 := {
+		11: 22
+		33: 44
+	}
+	im2 := {
+		55: 66
+		33: 999
+	}
+	merge_in_place(mut im1, im2)
+	assert im1 == {
+		11: 22
+		33: 999
+		55: 66
+	}
+	assert im2 == {
+		55: 66
+		33: 999
+	}
+}
+
+fn test_merge() {
+	m1 := {
+		'abc': 'def'
+		'aa':  'bb'
+	}
+	m2 := {
+		'xyz': 'zyx'
+		'aa':  'dd'
+	}
+	res := merge(m1, m2)
+	assert res == {
+		'abc': 'def'
+		'aa':  'dd'
+		'xyz': 'zyx'
+	}
+	assert m1 == {
+		'abc': 'def'
+		'aa':  'bb'
+	}
+	assert m2 == {
+		'xyz': 'zyx'
+		'aa':  'dd'
+	}
+	//
+	mut im1 := {
+		11: 22
+		33: 44
+	}
+	im2 := {
+		55: 66
+		33: 999
+	}
+	ires := merge(im1, im2)
+	assert im1 == {
+		11: 22
+		33: 44
+	}
+	assert im2 == {
+		55: 66
+		33: 999
+	}
+	assert ires == {
+		11: 22
+		33: 999
+		55: 66
+	}
+}