From de54a2b597723c779cf64e9dceb5cef09893ea06 Mon Sep 17 00:00:00 2001
From: Jonathan Poelen <jonathan.poelen@gmail.com>
Date: Mon, 19 Jun 2023 23:49:26 +0200
Subject: [PATCH] optimize mp_map_update (extract f from the struct to benefit
 from memoization)

compiler |       gcc-12       |      clang-15
before   | 0:00.73s - 270224K | 0:00.54s - 156112K
after    | 0:00.19s - 85004K  | 0:00.29s - 119232K

```cpp
using namespace boost::mp11;

template<class L, class M = mp_transform<mp_list, L>>
struct f { template<class I> using g = mp_map_update<M, mp_list<I>, mp_list>; };

template<class I, class L = mp_iota<I>> using test
  = mp_transform<f<L>::template g, L>;

using r1 = mp_transform<test, mp_iota_c<20>>;
```
---
 include/boost/mp11/map.hpp | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/include/boost/mp11/map.hpp b/include/boost/mp11/map.hpp
index b9581ac..a60119d 100644
--- a/include/boost/mp11/map.hpp
+++ b/include/boost/mp11/map.hpp
@@ -53,14 +53,20 @@ template<class M, class T> using mp_map_replace = typename detail::mp_map_replac
 namespace detail
 {
 
-template<class M, class T, template<class...> class F> struct mp_map_update_impl
+template<class T> struct mp_map_update_impl_f
 {
     template<class U> using _f = std::is_same<mp_first<T>, mp_first<U>>;
+};
 
+template<template<class...> class F> struct mp_map_update_impl_f3
+{
     // _f3<L<X, Y...>> -> L<X, F<X, Y...>>
     template<class L> using _f3 = mp_assign<L, mp_list<mp_first<L>, mp_rename<L, F> > >;
+};
 
-    using type = mp_if< mp_map_contains<M, mp_first<T>>, mp_transform_if<_f, _f3, M>, mp_push_back<M, T> >;
+template<class M, class T, template<class...> class F> struct mp_map_update_impl
+{
+    using type = mp_if< mp_map_contains<M, mp_first<T>>, mp_transform_if<mp_map_update_impl_f<T>::template _f, mp_map_update_impl_f3<F>::template _f3, M>, mp_push_back<M, T> >;
 };
 
 } // namespace detail