This should be in C++23, but some compilers/libraries still lack it.

lifetime.h

@@ -0,0 +1,39 @@
+static_assert( __cplusplus > 2020'00 );
+
+#pragma once
+
+#include <Alepha/Alepha.h>
+
+#include <cstddef>
+
+#include <type_traits>
+
+namespace Alepha::Hydrogen  ::detail:: lifetime_m
+{
+	inline namespace exports
+	{
+		// When C++23 arrives, just turn these into `using` statements.
+
+		template< typename T >
+		std::add_pointer_t< T >
+		start_lifetime_as( void *const mp ) noexcept
+		{
+			const auto raw= new( mp ) std::byte[ sizeof( T ) ];
+			const auto data= reinterpret_cast< std::add_pointer_t< T > >( raw );
+			return std::launder( data );
+		}
+
+		template< typename T >
+		std::add_pointer_t< std::add_const_t< T > >
+		start_lifetime_as( const void *const p ) noexcept
+		{
+			const auto mp= const_cast< void * >( p );
+			return start_lifetime_as< std::add_const_t< T > >( mp );
+		}
+	}
+}
+
+namespace Alepha::Hydrogen::inline exports::inline lifetime_m
+{
+	using namespace detail::lifetime_m::exports;
+}