From 2470a3fb40c08b0017d47e7e5a4e8e7255f65919 Mon Sep 17 00:00:00 2001
From: Héctor Ramón Jiménez <hector@hecrj.dev>
Date: Mon, 5 Feb 2024 21:34:35 +0100
Subject: Assert closure provided to `Subscription::map` is non-capturing

---
 futures/src/subscription.rs | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

(limited to 'futures')

diff --git a/futures/src/subscription.rs b/futures/src/subscription.rs
index 4d5a1192..1ee291c1 100644
--- a/futures/src/subscription.rs
+++ b/futures/src/subscription.rs
@@ -89,14 +89,22 @@ impl<Message> Subscription<Message> {
     }
 
     /// Transforms the [`Subscription`] output with the given function.
-    pub fn map<A>(
-        mut self,
-        f: impl Fn(Message) -> A + MaybeSend + Clone + 'static,
-    ) -> Subscription<A>
+    ///
+    /// # Panics
+    /// The closure provided must be a non-capturing closure. The method
+    /// will panic in debug mode otherwise.
+    pub fn map<F, A>(mut self, f: F) -> Subscription<A>
     where
         Message: 'static,
+        F: Fn(Message) -> A + MaybeSend + Clone + 'static,
         A: 'static,
     {
+        debug_assert!(
+            std::mem::size_of::<F>() == 0,
+            "the closure {} provided in `Subscription::map` is capturing",
+            std::any::type_name::<F>(),
+        );
+
         Subscription {
             recipes: self
                 .recipes
-- 
cgit