From cba156b44fb4ea084805974f8ecc5833d184c325 Mon Sep 17 00:00:00 2001
From: Thomas Altenbach <altenbach.thomas@gmail.com>
Date: Mon, 19 Oct 2026 02:23:19 +0200
Subject: [PATCH] Allow implicit conversions in variant's operator=

Reuse the converting constructor's alternative-selection helper in
operator=(T&&). Select the best non-narrowing implicit conversion and
reject ambiguous matches.

Note that contrary to std::variant's operator=, no constraint is added
to refuse types T for which is_assignable_v<TAlternative&, T> is false.
Indeed, there are existing tests that explicitly check that operator=
can be used with a non-assignable type.
---
 include/etl/private/variant_variadic.h | 12 +++++-------
 test/test_variant_variadic.cpp         |  7 +++++++
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/include/etl/private/variant_variadic.h b/include/etl/private/variant_variadic.h
index 8e7670df..7b2ac4be 100644
--- a/include/etl/private/variant_variadic.h
+++ b/include/etl/private/variant_variadic.h
@@ -1266,17 +1266,15 @@ namespace etl
     /// Move assignment operator for type.
     ///\param value The value to assign.
     //***************************************************************************
-    template <
-      typename T,
-      etl::enable_if_t<!etl::is_same<etl::remove_cvref_t<T>, variant>::value && etl::is_one_of<etl::remove_cvref_t<T>, TTypes...>::value, int> = 0>
+    template < typename T, etl::enable_if_t<!etl::is_same<etl::remove_cvref_t<T>, variant>::value, int> = 0,
+               size_t AlternativeIndex = private_variant::select_alternative_index<T, TTypes...>::value,
+               typename TAlternative = type_from_index<AlternativeIndex>, etl::enable_if_t<etl::is_constructible<TAlternative, T>::value, int> = 0>
     variant& operator=(T&& value)
     {
-      using type = etl::remove_cvref_t<T>;
-
       do_destroy();
-      do_construct<type>(etl::forward<T>(value));
+      do_construct<TAlternative>(etl::forward<T>(value));
 
-      type_id = index_of_type<type>::value;
+      type_id = AlternativeIndex;
 
       return *this;
     }
diff --git a/test/test_variant_variadic.cpp b/test/test_variant_variadic.cpp
index 8c8d6ac1..71881fd6 100644
--- a/test/test_variant_variadic.cpp
+++ b/test/test_variant_variadic.cpp
@@ -1468,12 +1468,19 @@ namespace
     //*************************************************************************
     TEST(test_assign_from_value)
     {
+      // No conversion required
       std::string        text("Some Text");
       test_variant_etl_3 variant_etl;
 
       variant_etl = text;
 
       CHECK_EQUAL(text, etl::get<std::string>(variant_etl));
+
+      // Conversion from float to double required
+      etl::variant<int, double> variant_double;
+      variant_double = 1.5f;
+
+      CHECK_EQUAL(1.5, etl::get<double>(variant_double));
     }
 
     //*************************************************************************