From d70897fee4fed3a7309ea5e19efa2b244c12412f Mon Sep 17 00:00:00 2001
From: Jonathan Poelen <jonathan.poelen@gmail.com>
Date: Sun, 9 Nov 2025 02:16:04 +0100
Subject: [PATCH] optimize mp_map_replace

compiler |      gcc-15        |     clang-20
before   | 0:00.39s - 114524K | 0:00.66s - 155888K
after    | 0:00.38s - 114140K | 0:00.64s - 155184K

```cpp
template<class I, class L = mp_transform<mp_list, mp_iota<I>>> using test
  = mp_map_replace<L, mp_list<I,I>>;

using r1 = mp_transform<test, mp_iota_c<120>>;
```
---
 include/boost/mp11/map.hpp | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/include/boost/mp11/map.hpp b/include/boost/mp11/map.hpp
index dc49795..0836507 100644
--- a/include/boost/mp11/map.hpp
+++ b/include/boost/mp11/map.hpp
@@ -46,9 +46,7 @@ template<template<class...> class M, class... U, class T> struct mp_map_replace_
 
 #else
 
-    template<class V> using _f = mp_if< std::is_same<mp_first<V>, K>, T, V >;
-
-    using type = mp_if< mp_map_contains<M<U...>, K>, M<_f<U>...>, M<U..., T> >;
+    using type = mp_if< mp_map_contains<M<U...>, K>, M<mp_if< std::is_same<mp_first<U>, K>, T, U >...>, M<U..., T> >;
 
 #endif
 };