From 0dd4e8c55d502f8f1d1131ed4c477d904a81ad76 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Wed, 11 Mar 2026 16:17:10 +0300
Subject: [PATCH] maps: compilation error when using `.to_array()` with a map
 whose value type is an interface (fixes #26567)

---
 vlib/maps/maps.v      | 31 +++++++++++++++++++++++++------
 vlib/maps/maps_test.v | 39 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+), 6 deletions(-)

diff --git a/vlib/maps/maps.v b/vlib/maps/maps.v
index 4d1873009..9a212f1eb 100644
--- a/vlib/maps/maps.v
+++ b/vlib/maps/maps.v
@@ -5,8 +5,14 @@ pub fn filter[K, V](m map[K]V, f fn (key K, val V) bool) map[K]V {
 	mut mp := map[K]V{}
 
 	for k, v in m {
-		if f(k, v) {
-			mp[k] = v
+		$if V is $interface {
+			if f(k, unsafe { v }) {
+				mp[k] = v
+			}
+		} $else {
+			if f(k, v) {
+				mp[k] = v
+			}
 		}
 	}
 
@@ -18,7 +24,11 @@ pub fn to_array[K, V, I](m map[K]V, f fn (key K, val V) I) []I {
 	mut a := []I{cap: m.len}
 
 	for k, v in m {
-		a << f(k, v)
+		$if V is $interface {
+			a << f(k, unsafe { v })
+		} $else {
+			a << f(k, v)
+		}
 	}
 
 	return a
@@ -29,7 +39,11 @@ pub fn flat_map[K, V, I](m map[K]V, f fn (key K, val V) []I) []I {
 	mut a := []I{cap: m.len}
 
 	for k, v in m {
-		a << f(k, v)
+		$if V is $interface {
+			a << f(k, unsafe { v })
+		} $else {
+			a << f(k, v)
+		}
 	}
 
 	return a
@@ -40,8 +54,13 @@ pub fn to_map[K, V, X, Y](m map[K]V, f fn (key K, val V) (X, Y)) map[X]Y {
 	mut mp := map[X]Y{}
 
 	for k, v in m {
-		x, y := f(k, v)
-		mp[x] = y
+		$if V is $interface {
+			x, y := f(k, unsafe { v })
+			mp[x] = y
+		} $else {
+			x, y := f(k, v)
+			mp[x] = y
+		}
 	}
 
 	return mp
diff --git a/vlib/maps/maps_test.v b/vlib/maps/maps_test.v
index 85869e191..96eb6ff81 100644
--- a/vlib/maps/maps_test.v
+++ b/vlib/maps/maps_test.v
@@ -1,5 +1,17 @@
 module maps
 
+interface TestValue {
+	value() string
+}
+
+struct TestValueImpl {
+	raw string
+}
+
+fn (v TestValueImpl) value() string {
+	return v.raw
+}
+
 fn test_filter() {
 	m1 := {
 		0: 'ab'
@@ -36,6 +48,33 @@ fn test_to_array() {
 	}) == ['abc', 'def', 'ghi']
 }
 
+fn test_helpers_with_interface_map_values() {
+	m1 := {
+		'a': TestValue(TestValueImpl{'bc'})
+		'd': TestValue(TestValueImpl{'ef'})
+		'g': TestValue(TestValueImpl{'hi'})
+	}
+	filtered := filter(m1, fn (k string, v TestValue) bool {
+		return k == 'a' || v.value() == 'ef'
+	})
+	assert filtered.len == 2
+	assert filtered['a'].value() == 'bc'
+	assert filtered['d'].value() == 'ef'
+	assert to_array(m1, fn (k string, v TestValue) string {
+		return '${k}${v.value()}'
+	}) == ['abc', 'def', 'ghi']
+	assert flat_map[string, TestValue, string](m1, fn (k string, v TestValue) []string {
+		return [k, v.value()]
+	}) == ['a', 'bc', 'd', 'ef', 'g', 'hi']
+	assert to_map[string, TestValue, string, string](m1, fn (k string, v TestValue) (string, string) {
+		return k, v.value()
+	}) == {
+		'a': 'bc'
+		'd': 'ef'
+		'g': 'hi'
+	}
+}
+
 fn test_flat_map() {
 	m1 := {
 		1: [2, 3]
-- 
2.39.5