From def67bba57e7cfdf9942bc2c88a4ce484963f9d2 Mon Sep 17 00:00:00 2001
From: Steven Le Rouzic <steven.lerouzic@gmail.com>
Date: Fri, 6 Sep 2024 23:22:18 +0200
Subject: maybe_uninit

---
 asl/BUILD.bazel            |  5 ++++-
 asl/annotations.hpp        | 11 +++++++++++
 asl/layout.hpp             | 29 +++++++++++++++++++++++++++++
 asl/maybe_uninit.hpp       | 44 ++++++++++++++++++++++++++++++++++++++++++++
 asl/maybe_uninit_tests.cpp |  7 +++++++
 asl/memory.hpp             |  8 ++++++++
 6 files changed, 103 insertions(+), 1 deletion(-)
 create mode 100644 asl/layout.hpp
 create mode 100644 asl/maybe_uninit.hpp
 create mode 100644 asl/maybe_uninit_tests.cpp
 create mode 100644 asl/memory.hpp

(limited to 'asl')

diff --git a/asl/BUILD.bazel b/asl/BUILD.bazel
index e5d5eb3..d7371c1 100644
--- a/asl/BUILD.bazel
+++ b/asl/BUILD.bazel
@@ -3,6 +3,9 @@ cc_library(
     hdrs = [
         "annotations.hpp",
         "integers.hpp",
+        "layout.hpp",
+        "maybe_uninit.hpp",
+        "memory.hpp",
         "meta.hpp",
         "option.hpp",
         "utility.hpp",
@@ -19,4 +22,4 @@ cc_library(
     deps = [
         ":asl",
     ],
-) for name in ["integers", "meta", "option", "utility"]]
+) for name in ["integers", "maybe_uninit", "meta", "option", "utility"]]
diff --git a/asl/annotations.hpp b/asl/annotations.hpp
index a94834d..c0d8f20 100644
--- a/asl/annotations.hpp
+++ b/asl/annotations.hpp
@@ -10,3 +10,14 @@
     #define ASL_NO_UNIQUE_ADDRESS [[no_unique_address]]
 #endif
 
+namespace asl
+{
+
+struct unsafe
+{
+    unsafe() = delete;
+    explicit unsafe(auto&&) {}
+};
+
+} // namespace asl
+
diff --git a/asl/layout.hpp b/asl/layout.hpp
new file mode 100644
index 0000000..5141456
--- /dev/null
+++ b/asl/layout.hpp
@@ -0,0 +1,29 @@
+#pragma once
+
+#include "asl/integers.hpp"
+#include "asl/meta.hpp"
+
+namespace asl
+{
+
+template<typename T>
+inline constexpr int64_t size_of = static_cast<int64_t>(sizeof(T));
+
+template<typename T>
+inline constexpr int64_t align_of = static_cast<int64_t>(alignof(T));
+
+struct layout
+{
+    int64_t size;
+    int64_t align;
+
+    constexpr bool operator==(const layout&) const = default;
+
+    template<is_object T>
+    static constexpr layout of()
+    {
+        return layout{ size_of<T>, align_of<T> };
+    }
+};
+
+} // namespace asl
diff --git a/asl/maybe_uninit.hpp b/asl/maybe_uninit.hpp
new file mode 100644
index 0000000..ffbbb1c
--- /dev/null
+++ b/asl/maybe_uninit.hpp
@@ -0,0 +1,44 @@
+#pragma once
+
+#include "asl/annotations.hpp"
+#include "asl/layout.hpp"
+#include "asl/memory.hpp"
+#include "asl/meta.hpp"
+
+namespace asl
+{
+
+template<is_object T>
+class alignas(align_of<T>) maybe_uninit
+{
+    char m_storage[size_of<T>];
+
+public:
+    constexpr void* uninit_ptr() const { return m_storage; }
+
+    // @Safety Pointer must only be accessed when in initialized state.
+    constexpr const T* init_ptr(unsafe) const { return reinterpret_cast<const T*>(m_storage); }
+    constexpr       T* init_ptr(unsafe)       { return reinterpret_cast<      T*>(m_storage); }
+
+    // @Safety Reference must only be accessed when in initialized state.
+    constexpr const T& as_init(unsafe) const { return *reinterpret_cast<const T*>(m_storage); }
+    constexpr       T& as_init(unsafe)       { return *reinterpret_cast<      T*>(m_storage); }
+
+    // @Safety Must be called only when in uninitialized state.
+    template<typename... Args>
+    inline void init(unsafe, Args&&... args)
+    {
+        new(uninit_ptr()) T(ASL_FWD(args)...);
+    }
+
+    // @Safety Must be called only when in initialized state.
+    inline void uninit(unsafe)
+    {
+        if constexpr (!trivially_destructible<T>)
+        {
+            init_ptr(unsafe("Caller has checked init state"))->~T();
+        }
+    }
+};
+
+} // namespace asl
diff --git a/asl/maybe_uninit_tests.cpp b/asl/maybe_uninit_tests.cpp
new file mode 100644
index 0000000..7efeff0
--- /dev/null
+++ b/asl/maybe_uninit_tests.cpp
@@ -0,0 +1,7 @@
+#include "asl/maybe_uninit.hpp"
+
+static_assert(asl::layout::of<int>() == asl::layout::of<asl::maybe_uninit<int>>());
+static_assert(asl::size_of<int> == asl::size_of<asl::maybe_uninit<int>>);
+static_assert(asl::align_of<int> == asl::align_of<asl::maybe_uninit<int>>);
+
+int main() { return 0; }
diff --git a/asl/memory.hpp b/asl/memory.hpp
new file mode 100644
index 0000000..33fa819
--- /dev/null
+++ b/asl/memory.hpp
@@ -0,0 +1,8 @@
+#pragma once
+
+#include "asl/integers.hpp"
+
+constexpr void* operator new(uint64_t, void* ptr)
+{
+    return ptr;
+}
-- 
cgit