From 51e562411c4f09ede10521f305765ddd89f5994a Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Wed, 25 Mar 2026 16:42:19 +0300
Subject: [PATCH] checker: fix passing function as argument to vec.mul_scalar
 (fixes #25829)

---
 vlib/v/checker/checker.v                             |  4 ++++
 vlib/v/checker/tests/cast_function_to_number_err.out |  6 ++++++
 vlib/v/checker/tests/cast_function_to_number_err.vv  | 10 ++++++++++
 3 files changed, 20 insertions(+)
 create mode 100644 vlib/v/checker/tests/cast_function_to_number_err.out
 create mode 100644 vlib/v/checker/tests/cast_function_to_number_err.vv

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index df157ec49..697b25191 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -4970,6 +4970,10 @@ fn (mut c Checker) cast_expr(mut node ast.CastExpr) ast.Type {
 				c.error('invalid casting value to function', node.pos)
 			}
 		}
+	} else if final_from_sym.kind == .function && final_to_sym.is_number() {
+		fnexpr := node.expr.str()
+		tt := c.table.type_to_str(to_type)
+		c.error('cannot cast function `${fnexpr}` to `${tt}`', node.pos)
 	}
 	if to_type.is_ptr() && to_sym.kind == .alias && from_sym.kind == .map {
 		c.error('cannot cast to alias pointer `${c.table.type_to_str(to_type)}` because `${c.table.type_to_str(from_type)}` is a value',
diff --git a/vlib/v/checker/tests/cast_function_to_number_err.out b/vlib/v/checker/tests/cast_function_to_number_err.out
new file mode 100644
index 000000000..7a2ecf565
--- /dev/null
+++ b/vlib/v/checker/tests/cast_function_to_number_err.out
@@ -0,0 +1,6 @@
+vlib/v/checker/tests/cast_function_to_number_err.vv:9:10: error: cannot cast function `a.magnitude` to `f64`
+    7 | fn main() {
+    8 |     a := VecLike{}
+    9 |     println(f64(a.magnitude))
+      |             ~~~~~~~~~~~~~~~~
+   10 | }
diff --git a/vlib/v/checker/tests/cast_function_to_number_err.vv b/vlib/v/checker/tests/cast_function_to_number_err.vv
new file mode 100644
index 000000000..ef9f29d44
--- /dev/null
+++ b/vlib/v/checker/tests/cast_function_to_number_err.vv
@@ -0,0 +1,10 @@
+struct VecLike {}
+
+fn (v VecLike) magnitude() f64 {
+	return 1.0
+}
+
+fn main() {
+	a := VecLike{}
+	println(f64(a.magnitude))
+}
-- 
2.39.5