Refactor FlexArray

This avoids using an array of 1 as a flexible array member, and instead uses a
span to reference the memory after itself.

3 files changed, 114 insertions, 116 deletions

diff --git a/common/almalloc.h b/common/almalloc.h
index 288b5075..8a976aae 100644
--- a/common/almalloc.h
+++ b/common/almalloc.h
@@ -127,122 +127,6 @@ constexpr T* construct_at(T *ptr, Args&& ...args)
     noexcept(std::is_nothrow_constructible<T, Args...>::value)
 { return ::new(static_cast<void*>(ptr)) T{std::forward<Args>(args)...}; }
 
-
-/* Storage for flexible array data. This is trivially destructible if type T is
- * trivially destructible.
- */
-template<typename T, size_t alignment, bool = std::is_trivially_destructible<T>::value>
-struct FlexArrayStorage {
-    const size_t mSize;
-    union {
-        char mDummy;
-        alignas(alignment) T mArray[1];
-    };
-
-    static constexpr size_t Sizeof(size_t count, size_t base=0u) noexcept
-    {
-        const size_t len{sizeof(T)*count};
-        return std::max(offsetof(FlexArrayStorage,mArray)+len, sizeof(FlexArrayStorage)) + base;
-    }
-
-    FlexArrayStorage(size_t size) : mSize{size}
-    { std::uninitialized_default_construct_n(mArray, mSize); }
-    ~FlexArrayStorage() = default;
-
-    FlexArrayStorage(const FlexArrayStorage&) = delete;
-    FlexArrayStorage& operator=(const FlexArrayStorage&) = delete;
-};
-
-template<typename T, size_t alignment>
-struct FlexArrayStorage<T,alignment,false> {
-    const size_t mSize;
-    union {
-        char mDummy;
-        alignas(alignment) T mArray[1];
-    };
-
-    static constexpr size_t Sizeof(size_t count, size_t base) noexcept
-    {
-        const size_t len{sizeof(T)*count};
-        return std::max(offsetof(FlexArrayStorage,mArray)+len, sizeof(FlexArrayStorage)) + base;
-    }
-
-    FlexArrayStorage(size_t size) : mSize{size}
-    { std::uninitialized_default_construct_n(mArray, mSize); }
-    ~FlexArrayStorage() { std::destroy_n(mArray, mSize); }
-
-    FlexArrayStorage(const FlexArrayStorage&) = delete;
-    FlexArrayStorage& operator=(const FlexArrayStorage&) = delete;
-};
-
-/* A flexible array type. Used either standalone or at the end of a parent
- * struct, with placement new, to have a run-time-sized array that's embedded
- * with its size.
- */
-template<typename T, size_t alignment=alignof(T)>
-struct FlexArray {
-    using element_type = T;
-    using value_type = std::remove_cv_t<T>;
-    using index_type = size_t;
-    using difference_type = ptrdiff_t;
-
-    using pointer = T*;
-    using const_pointer = const T*;
-    using reference = T&;
-    using const_reference = const T&;
-
-    using iterator = pointer;
-    using const_iterator = const_pointer;
-    using reverse_iterator = std::reverse_iterator<iterator>;
-    using const_reverse_iterator = std::reverse_iterator<const_iterator>;
-
-    using Storage_t_ = FlexArrayStorage<element_type,alignment>;
-
-    Storage_t_ mStore;
-
-    static constexpr index_type Sizeof(index_type count, index_type base=0u) noexcept
-    { return Storage_t_::Sizeof(count, base); }
-    static std::unique_ptr<FlexArray> Create(index_type count)
-    {
-        void *ptr{al_calloc(alignof(FlexArray), Sizeof(count))};
-        return std::unique_ptr<FlexArray>{al::construct_at(static_cast<FlexArray*>(ptr), count)};
-    }
-
-    FlexArray(index_type size) : mStore{size} { }
-    ~FlexArray() = default;
-
-    [[nodiscard]] auto size() const noexcept -> index_type { return mStore.mSize; }
-    [[nodiscard]] auto empty() const noexcept -> bool { return mStore.mSize == 0; }
-
-    [[nodiscard]] auto data() noexcept -> pointer { return mStore.mArray; }
-    [[nodiscard]] auto data() const noexcept -> const_pointer { return mStore.mArray; }
-
-    [[nodiscard]] auto operator[](index_type i) noexcept -> reference { return mStore.mArray[i]; }
-    [[nodiscard]] auto operator[](index_type i) const noexcept -> const_reference { return mStore.mArray[i]; }
-
-    [[nodiscard]] auto front() noexcept -> reference { return mStore.mArray[0]; }
-    [[nodiscard]] auto front() const noexcept -> const_reference { return mStore.mArray[0]; }
-
-    [[nodiscard]] auto back() noexcept -> reference { return mStore.mArray[mStore.mSize-1]; }
-    [[nodiscard]] auto back() const noexcept -> const_reference { return mStore.mArray[mStore.mSize-1]; }
-
-    [[nodiscard]] auto begin() noexcept -> iterator { return mStore.mArray; }
-    [[nodiscard]] auto begin() const noexcept -> const_iterator { return mStore.mArray; }
-    [[nodiscard]] auto cbegin() const noexcept -> const_iterator { return mStore.mArray; }
-    [[nodiscard]] auto end() noexcept -> iterator { return mStore.mArray + mStore.mSize; }
-    [[nodiscard]] auto end() const noexcept -> const_iterator { return mStore.mArray + mStore.mSize; }
-    [[nodiscard]] auto cend() const noexcept -> const_iterator { return mStore.mArray + mStore.mSize; }
-
-    [[nodiscard]] auto rbegin() noexcept -> reverse_iterator { return end(); }
-    [[nodiscard]] auto rbegin() const noexcept -> const_reverse_iterator { return end(); }
-    [[nodiscard]] auto crbegin() const noexcept -> const_reverse_iterator { return cend(); }
-    [[nodiscard]] auto rend() noexcept -> reverse_iterator { return begin(); }
-    [[nodiscard]] auto rend() const noexcept -> const_reverse_iterator { return begin(); }
-    [[nodiscard]] auto crend() const noexcept -> const_reverse_iterator { return cbegin(); }
-
-    DEF_PLACE_NEWDEL()
-};
-
 } // namespace al
 
 #endif /* AL_MALLOC_H */
diff --git a/common/flexarray.h b/common/flexarray.h
new file mode 100644
index 00000000..d02a7342
--- /dev/null
+++ b/common/flexarray.h
@@ -0,0 +1,113 @@
+#ifndef AL_FLEXARRAY_H
+#define AL_FLEXARRAY_H
+
+#include <cstddef>
+#include <type_traits>
+
+#include "almalloc.h"
+#include "alspan.h"
+
+namespace al {
+
+/* Storage for flexible array data. This is trivially destructible if type T is
+ * trivially destructible.
+ */
+template<typename T, size_t alignment, bool = std::is_trivially_destructible<T>::value>
+struct FlexArrayStorage {
+    alignas(alignment) const ::al::span<T> mData;
+
+    static constexpr size_t Sizeof(size_t count, size_t base=0u) noexcept
+    { return sizeof(FlexArrayStorage) + sizeof(T)*count + base; }
+
+    FlexArrayStorage(size_t size) : mData{::new(static_cast<void*>(this+1)) T[size], size} { }
+    ~FlexArrayStorage() = default;
+
+    FlexArrayStorage(const FlexArrayStorage&) = delete;
+    FlexArrayStorage& operator=(const FlexArrayStorage&) = delete;
+};
+
+template<typename T, size_t alignment>
+struct FlexArrayStorage<T,alignment,false> {
+    alignas(alignment) const ::al::span<T> mData;
+
+    static constexpr size_t Sizeof(size_t count, size_t base=0u) noexcept
+    { return sizeof(FlexArrayStorage) + sizeof(T)*count + base; }
+
+    FlexArrayStorage(size_t size) : mData{::new(static_cast<void*>(this+1)) T[size], size} { }
+    ~FlexArrayStorage() { std::destroy(mData.begin(), mData.end()); }
+
+    FlexArrayStorage(const FlexArrayStorage&) = delete;
+    FlexArrayStorage& operator=(const FlexArrayStorage&) = delete;
+};
+
+/* A flexible array type. Used either standalone or at the end of a parent
+ * struct, with placement new, to have a run-time-sized array that's embedded
+ * with its size.
+ */
+template<typename T, size_t alignment=alignof(T)>
+struct FlexArray {
+    using element_type = T;
+    using value_type = std::remove_cv_t<T>;
+    using index_type = size_t;
+    using difference_type = ptrdiff_t;
+
+    using pointer = T*;
+    using const_pointer = const T*;
+    using reference = T&;
+    using const_reference = const T&;
+
+    using iterator = pointer;
+    using const_iterator = const_pointer;
+    using reverse_iterator = std::reverse_iterator<iterator>;
+    using const_reverse_iterator = std::reverse_iterator<const_iterator>;
+
+    using Storage_t_ = FlexArrayStorage<element_type,alignment>;
+
+    Storage_t_ mStore;
+
+    static constexpr index_type Sizeof(index_type count, index_type base=0u) noexcept
+    { return Storage_t_::Sizeof(count, base); }
+    static std::unique_ptr<FlexArray> Create(index_type count)
+    {
+        void *ptr{al_calloc(alignof(FlexArray), Sizeof(count))};
+        return std::unique_ptr<FlexArray>{al::construct_at(static_cast<FlexArray*>(ptr), count)};
+    }
+
+    FlexArray(index_type size) : mStore{size} { }
+    ~FlexArray() = default;
+
+    [[nodiscard]] auto size() const noexcept -> index_type { return mStore.mData.size(); }
+    [[nodiscard]] auto empty() const noexcept -> bool { return mStore.mData.empty(); }
+
+    [[nodiscard]] auto data() noexcept -> pointer { return mStore.mData.data(); }
+    [[nodiscard]] auto data() const noexcept -> const_pointer { return mStore.mData.data(); }
+
+    [[nodiscard]] auto operator[](index_type i) noexcept -> reference { return mStore.mData[i]; }
+    [[nodiscard]] auto operator[](index_type i) const noexcept -> const_reference { return mStore.mData[i]; }
+
+    [[nodiscard]] auto front() noexcept -> reference { return mStore.mData.front(); }
+    [[nodiscard]] auto front() const noexcept -> const_reference { return mStore.mData.front(); }
+
+    [[nodiscard]] auto back() noexcept -> reference { return mStore.mData.back(); }
+    [[nodiscard]] auto back() const noexcept -> const_reference { return mStore.mData.back(); }
+
+    [[nodiscard]] auto begin() noexcept -> iterator { return mStore.mData.begin(); }
+    [[nodiscard]] auto begin() const noexcept -> const_iterator { return mStore.mData.begin(); }
+    [[nodiscard]] auto cbegin() const noexcept -> const_iterator { return mStore.mData.cbegin(); }
+    [[nodiscard]] auto end() noexcept -> iterator { return mStore.mData.end(); }
+    [[nodiscard]] auto end() const noexcept -> const_iterator { return mStore.mData.end(); }
+    [[nodiscard]] auto cend() const noexcept -> const_iterator { return mStore.mData.cend(); }
+
+    [[nodiscard]] auto rbegin() noexcept -> reverse_iterator { return end(); }
+    [[nodiscard]] auto rbegin() const noexcept -> const_reverse_iterator { return end(); }
+    [[nodiscard]] auto crbegin() const noexcept -> const_reverse_iterator { return cend(); }
+    [[nodiscard]] auto rend() noexcept -> reverse_iterator { return begin(); }
+    [[nodiscard]] auto rend() const noexcept -> const_reverse_iterator { return begin(); }
+    [[nodiscard]] auto crend() const noexcept -> const_reverse_iterator { return cbegin(); }
+
+    DEF_PLACE_NEWDEL()
+};
+
+} // namespace al
+
+#endif /* AL_FLEXARRAY_H */
diff --git a/common/ringbuffer.h b/common/ringbuffer.h
index 718238a3..a2b820eb 100644
--- a/common/ringbuffer.h
+++ b/common/ringbuffer.h
@@ -7,6 +7,7 @@
 #include <utility>
 
 #include "almalloc.h"
+#include "flexarray.h"
 
 
 /* NOTE: This lockless ringbuffer implementation is copied from JACK, extended