From e6a1cc363c54e5bcbf0381cd3fade6ef86c33f9d Mon Sep 17 00:00:00 2001
From: Herb Sutter <herb.sutter@gmail.com>
Date: Fri, 20 Oct 2023 15:07:45 -0700
Subject: [PATCH] Make `new` use list initialization if available

This enables uses like `new<std::array<int,5>>(1, 2, 3, 4, 5)` which didn't work before (not even with P0960)

See #740

Note: I chose "use list init if available, else fall back to non-list init" instead of "use paren init if available, else fall back to list init" so that we would get consistent results for initializing a `new<std::vector<int>>` with `(10)`, `(10, 20)`, `(10, 20, 30)`, etc. (i.e., no surprise for `(10, 20)`)
---
 include/cpp2util.h                               | 16 ++++++++++++++--
 .../test-results/msvc-2022/MSVC-version.output   |  2 +-
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/include/cpp2util.h b/include/cpp2util.h
index a089e59cb..354093ea9 100644
--- a/include/cpp2util.h
+++ b/include/cpp2util.h
@@ -556,14 +556,26 @@ auto Typeid() -> decltype(auto) {
 struct {
     template<typename T>
     [[nodiscard]] auto cpp2_new(auto&& ...args) const -> std::unique_ptr<T> {
-        return std::make_unique<T>(CPP2_FORWARD(args)...);
+        if constexpr (requires { T{CPP2_FORWARD(args)...}; }) {
+            //  This is because apparently make_unique can't deal with list
+            //  initialization of aggregates, even after P0960
+            return std::unique_ptr<T>( new T{CPP2_FORWARD(args)...} );
+        }
+        else {
+            return std::make_unique<T>(CPP2_FORWARD(args)...);
+        }
     }
 } inline unique;
 
 [[maybe_unused]] struct {
     template<typename T>
     [[nodiscard]] auto cpp2_new(auto&& ...args) const -> std::shared_ptr<T> {
-        return std::make_shared<T>(CPP2_FORWARD(args)...);
+        if constexpr (requires { T{CPP2_FORWARD(args)...}; }) {
+            return unique.cpp2_new<T>(CPP2_FORWARD(args)...);
+        }
+        else {
+            return std::make_shared<T>(CPP2_FORWARD(args)...);
+        }
     }
 } inline shared;
 
diff --git a/regression-tests/test-results/msvc-2022/MSVC-version.output b/regression-tests/test-results/msvc-2022/MSVC-version.output
index bd44f14bb..1559c12b5 100644
--- a/regression-tests/test-results/msvc-2022/MSVC-version.output
+++ b/regression-tests/test-results/msvc-2022/MSVC-version.output
@@ -1,3 +1,3 @@
-Microsoft (R) C/C++ Optimizing Compiler Version 19.37.32824 for x86
+Microsoft (R) C/C++ Optimizing Compiler Version 19.37.32825 for x86
 Copyright (C) Microsoft Corporation.  All rights reserved.