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modules/serialization/include/tw/serial/BinaryBuffer.hpp

@@ -0,0 +1,90 @@
+#pragma once
+
+#include <cassert>
+#include <cstddef>
+#include <cstdint>
+#include <cstring>
+#include <span>
+#include <vector>
+
+namespace tw::serial {
+
+/**
+ * A flat, pre-allocated, non-owning-after-construction byte buffer used as the
+ * backing store for BinaryWriter.
+ *
+ * Design goals:
+ *  - Zero heap allocation after the initial reserve().
+ *  - reset() in O(1) — just rewinds the write cursor.
+ *  - view() gives a read-only span over written bytes, usable directly as a
+ *    UDP payload without any copy.
+ *  - Not thread-safe: one buffer per client, reused every frame.
+ */
+class BinaryBuffer {
+    std::vector<std::byte> m_storage;
+    std::size_t            m_pos{ 0 };
+
+public:
+    BinaryBuffer() = default;
+
+    explicit BinaryBuffer(std::size_t capacity) {
+        m_storage.resize(capacity);
+    }
+
+    // Reserve at least `capacity` bytes.  May only grow, never shrinks.
+    void reserve(std::size_t capacity) {
+        if (capacity > m_storage.size()) {
+            m_storage.resize(capacity);
+        }
+    }
+
+    // Reset write cursor to 0.  Does NOT zero memory — intentional for perf.
+    void reset() noexcept { m_pos = 0; }
+
+    std::size_t size()     const noexcept { return m_pos; }
+    std::size_t capacity() const noexcept { return m_storage.size(); }
+    bool        empty()    const noexcept { return m_pos == 0; }
+
+    // Returns a view over bytes written so far.  Valid until the next write or reset.
+    std::span<const std::byte> view() const noexcept {
+        return { m_storage.data(), m_pos };
+    }
+
+    // Returns a mutable span over bytes written so far.
+    std::span<std::byte> mutable_view() noexcept {
+        return { m_storage.data(), m_pos };
+    }
+
+    /**
+     * Append `n` raw bytes from `src`.
+     * Asserts in debug; in release callers must pre-reserve enough space.
+     */
+    void append(const void* src, std::size_t n) noexcept {
+        assert(m_pos + n <= m_storage.size() && "BinaryBuffer overflow — call reserve() with a larger capacity");
+        std::memcpy(m_storage.data() + m_pos, src, n);
+        m_pos += n;
+    }
+
+    /**
+     * Reserve `n` bytes in-place and return a pointer to them.
+     * Lets callers write directly (e.g. via placement algorithms) without a
+     * temporary.
+     */
+    std::byte* claim(std::size_t n) noexcept {
+        assert(m_pos + n <= m_storage.size() && "BinaryBuffer overflow — call reserve() with a larger capacity");
+        std::byte* ptr = m_storage.data() + m_pos;
+        m_pos += n;
+        return ptr;
+    }
+
+    /**
+     * Patch a previously written 4-byte field at `offset`.
+     * Useful for writing a length prefix before the payload is known.
+     */
+    void patch_u32(std::size_t offset, uint32_t value) noexcept {
+        assert(offset + sizeof(uint32_t) <= m_pos);
+        std::memcpy(m_storage.data() + offset, &value, sizeof(uint32_t));
+    }
+};
+
+} // namespace tw::serial

modules/serialization/include/tw/serial/Codec.hpp

@@ -0,0 +1,222 @@
+#pragma once
+
+/**
+ * tw::serial — generic, zero-allocation binary codec
+ * ====================================================
+ *
+ * Extensibility model (ADL / explicit specialisation)
+ * ---------------------------------------------------
+ * To make a type T serialisable, either:
+ *
+ *   a) Specialise tw::serial::Codec<T>:
+ *
+ *       template<>
+ *       struct tw::serial::Codec<MyType> {
+ *           static void encode(BinaryWriter& w, const MyType& v);
+ *           static MyType decode(BinaryReader& r);
+ *       };
+ *
+ *   b) Or provide free functions in the same namespace as T:
+ *
+ *       void tw_serial_encode(BinaryWriter& w, const MyType& v);
+ *       MyType tw_serial_decode(BinaryReader& r, std::type_identity<MyType>);
+ *
+ * The BinaryWriter/BinaryReader forward-declared here are defined in
+ * BinaryWriter.hpp / BinaryReader.hpp.  Codec.hpp itself is header-only
+ * and has no external dependencies beyond the C++ standard library.
+ */
+
+#include "BinaryBuffer.hpp"
+
+#include <bit>
+#include <concepts>
+#include <cstdint>
+#include <cstring>
+#include <span>
+#include <type_traits>
+
+namespace tw::serial {
+
+// Forward declarations
+class BinaryWriter;
+class BinaryReader;
+
+// ── Primary template — intentionally incomplete so missing specialisations
+//    produce a clear compiler error rather than silent wrong behaviour.
+template<typename T>
+struct Codec;
+
+// ── Concept: a type is Encodable if Codec<T>::encode exists.
+template<typename T>
+concept Encodable = requires(BinaryWriter & w, const T & v) {
+    Codec<T>::encode(w, v);
+};
+
+// ── Concept: a type is Decodable if Codec<T>::decode exists.
+template<typename T>
+concept Decodable = requires(BinaryReader & r) {
+    { Codec<T>::decode(r) } -> std::same_as<T>;
+};
+
+// ──────────────────────────────────────────────────────────────────────────
+// BinaryWriter
+// ──────────────────────────────────────────────────────────────────────────
+
+/**
+ * Thin write-cursor over a BinaryBuffer.
+ *
+ * All write operations are branch-free memcpy paths for trivially-copyable
+ * types.  The buffer itself holds the memory; the writer is just a cursor.
+ */
+class BinaryWriter {
+    BinaryBuffer& m_buf;
+
+public:
+    explicit BinaryWriter(BinaryBuffer& buf) noexcept : m_buf(buf) {}
+
+    // ── Raw bytes ────────────────────────────────────────────────────────
+
+    void write_bytes(const void* src, std::size_t n) noexcept {
+        m_buf.append(src, n);
+    }
+
+    void write_bytes(std::span<const std::byte> data) noexcept {
+        m_buf.append(data.data(), data.size());
+    }
+
+    // ── Primitive scalar ─────────────────────────────────────────────────
+
+    template<typename T>
+        requires std::is_trivially_copyable_v<T>
+    void write(const T& value) noexcept {
+        m_buf.append(&value, sizeof(T));
+    }
+
+    // ── Codec-dispatched write ────────────────────────────────────────────
+
+    template<Encodable T>
+    void encode(const T& value) {
+        Codec<T>::encode(*this, value);
+    }
+
+    // ── Cursor helpers ────────────────────────────────────────────────────
+
+    /** Returns the current write position (useful for length-prefix patching). */
+    std::size_t pos() const noexcept { return m_buf.size(); }
+
+    /** Reserve a 4-byte slot at the current position, return its offset. */
+    std::size_t reserve_u32() noexcept {
+        std::size_t offset = m_buf.size();
+        uint32_t placeholder = 0;
+        m_buf.append(&placeholder, sizeof(uint32_t));
+        return offset;
+    }
+
+    /** Patch a 4-byte slot previously reserved with reserve_u32(). */
+    void patch_u32(std::size_t offset, uint32_t value) noexcept {
+        m_buf.patch_u32(offset, value);
+    }
+
+    BinaryBuffer&       buffer()       noexcept { return m_buf; }
+    const BinaryBuffer& buffer() const noexcept { return m_buf; }
+
+    void reset() noexcept {
+        m_buf.reset();
+    }
+
+};
+
+// ──────────────────────────────────────────────────────────────────────────
+// BinaryReader
+// ──────────────────────────────────────────────────────────────────────────
+
+/**
+ * Read-cursor over an immutable span of bytes.
+ *
+ * Designed for deserialisation on the client side; does not own memory.
+ * All reads advance an internal cursor.  Out-of-bounds reads assert in
+ * debug and invoke undefined behaviour in release (callers must validate
+ * message length before feeding it to a BinaryReader).
+ */
+class BinaryReader {
+    const std::byte* m_ptr;
+    std::size_t      m_remaining;
+
+public:
+    explicit BinaryReader(std::span<const std::byte> data) noexcept
+        : m_ptr(data.data()), m_remaining(data.size()) {}
+
+    // ── Raw bytes ────────────────────────────────────────────────────────
+
+    void read_bytes(void* dst, std::size_t n) noexcept {
+        assert(n <= m_remaining && "BinaryReader underflow");
+        std::memcpy(dst, m_ptr, n);
+        m_ptr      += n;
+        m_remaining -= n;
+    }
+
+    std::span<const std::byte> read_bytes(std::size_t n) noexcept {
+        assert(n <= m_remaining && "BinaryReader underflow");
+        auto span = std::span<const std::byte>{ m_ptr, n };
+        m_ptr      += n;
+        m_remaining -= n;
+        return span;
+    }
+
+    // ── Primitive scalar ─────────────────────────────────────────────────
+
+    template<typename T>
+        requires std::is_trivially_copyable_v<T>
+    T read() noexcept {
+        T value;
+        read_bytes(&value, sizeof(T));
+        return value;
+    }
+
+    // ── Codec-dispatched read ─────────────────────────────────────────────
+
+    template<Decodable T>
+    T decode() {
+        return Codec<T>::decode(*this);
+    }
+
+    // ── State ─────────────────────────────────────────────────────────────
+
+    std::size_t remaining() const noexcept { return m_remaining; }
+    bool        empty()     const noexcept { return m_remaining == 0; }
+};
+
+// ──────────────────────────────────────────────────────────────────────────
+// Built-in Codec specialisations for C++ primitives
+// ──────────────────────────────────────────────────────────────────────────
+
+// All fixed-width integer and float types that are trivially copyable get
+// a direct memcpy codec — no varint encoding, deliberately, because we are
+// optimising for throughput not wire-size (and positions are floats anyway).
+
+#define TW_SERIAL_TRIVIAL_CODEC(T)                                      \
+    template<>                                                           \
+    struct Codec<T> {                                                     \
+        static void encode(BinaryWriter& w, const T& v) noexcept {      \
+            w.write(v);                                                  \
+        }                                                                 \
+        static T decode(BinaryReader& r) noexcept {                      \
+            return r.read<T>();                                          \
+        }                                                                 \
+    }
+
+TW_SERIAL_TRIVIAL_CODEC(bool);
+TW_SERIAL_TRIVIAL_CODEC(uint8_t);
+TW_SERIAL_TRIVIAL_CODEC(uint16_t);
+TW_SERIAL_TRIVIAL_CODEC(uint32_t);
+TW_SERIAL_TRIVIAL_CODEC(uint64_t);
+TW_SERIAL_TRIVIAL_CODEC(int8_t);
+TW_SERIAL_TRIVIAL_CODEC(int16_t);
+TW_SERIAL_TRIVIAL_CODEC(int32_t);
+TW_SERIAL_TRIVIAL_CODEC(int64_t);
+TW_SERIAL_TRIVIAL_CODEC(float);
+TW_SERIAL_TRIVIAL_CODEC(double);
+
+#undef TW_SERIAL_TRIVIAL_CODEC
+
+} // namespace tw::serial

modules/serialization/include/tw/serial/EnttCodec.hpp

@@ -0,0 +1,30 @@
+#pragma once
+
+/**
+ * Codec specialisation for entt::entity.
+ *
+ * Wire format: uint32_t  (the raw entity storage value, 4 bytes).
+ *
+ * EnTT entities are 32-bit identifiers internally (version bits + index bits).
+ * We transmit the raw value and let the receiver reconstruct via
+ * static_cast<entt::entity>(id).
+ */
+
+#include "Codec.hpp"
+
+#include <entt/entt.hpp>
+
+namespace tw::serial {
+
+template<>
+struct Codec<entt::entity> {
+    static void encode(BinaryWriter& w, const entt::entity& e) noexcept {
+        auto raw = static_cast<uint32_t>(e);
+        w.write(raw);
+    }
+    static entt::entity decode(BinaryReader& r) noexcept {
+        return static_cast<entt::entity>(r.read<uint32_t>());
+    }
+};
+
+} // namespace tw::serial

modules/serialization/include/tw/serial/GlmCodec.hpp

@@ -0,0 +1,77 @@
+#pragma once
+
+/**
+ * Codec specialisations for GLM types.
+ *
+ * Include this header in any translation unit that needs to
+ * encode/decode GLM vectors or matrices.
+ *
+ * Wire format (little-endian, matches the host layout on x86/ARM LE):
+ *   vec2  — 2 × float  (8 bytes)
+ *   vec3  — 3 × float  (12 bytes)
+ *   vec4  — 4 × float  (16 bytes)
+ *   mat4  — 16 × float (64 bytes, column-major, matching GLM's default)
+ */
+
+#include "Codec.hpp"
+
+#include <glm/vec2.hpp>
+#include <glm/vec3.hpp>
+#include <glm/vec4.hpp>
+#include <glm/mat4x4.hpp>
+
+namespace tw::serial {
+
+template<>
+struct Codec<glm::vec2> {
+    static void encode(BinaryWriter& w, const glm::vec2& v) noexcept {
+        w.write(v.x);
+        w.write(v.y);
+    }
+    static glm::vec2 decode(BinaryReader& r) noexcept {
+        glm::vec2 v;
+        v.x = r.read<float>();
+        v.y = r.read<float>();
+        return v;
+    }
+};
+
+template<>
+struct Codec<glm::vec3> {
+    static void encode(BinaryWriter& w, const glm::vec3& v) noexcept {
+        // vec3 is 3 contiguous floats in GLM's layout
+        w.write_bytes(&v.x, 3 * sizeof(float));
+    }
+    static glm::vec3 decode(BinaryReader& r) noexcept {
+        glm::vec3 v;
+        r.read_bytes(&v.x, 3 * sizeof(float));
+        return v;
+    }
+};
+
+template<>
+struct Codec<glm::vec4> {
+    static void encode(BinaryWriter& w, const glm::vec4& v) noexcept {
+        w.write_bytes(&v.x, 4 * sizeof(float));
+    }
+    static glm::vec4 decode(BinaryReader& r) noexcept {
+        glm::vec4 v;
+        r.read_bytes(&v.x, 4 * sizeof(float));
+        return v;
+    }
+};
+
+template<>
+struct Codec<glm::mat4> {
+    static void encode(BinaryWriter& w, const glm::mat4& m) noexcept {
+        // GLM mat4 is column-major; 16 contiguous floats
+        w.write_bytes(&m[0][0], 16 * sizeof(float));
+    }
+    static glm::mat4 decode(BinaryReader& r) noexcept {
+        glm::mat4 m;
+        r.read_bytes(&m[0][0], 16 * sizeof(float));
+        return m;
+    }
+};
+
+} // namespace tw::serial

modules/serialization/include/tw/serial/Serial.hpp

@@ -0,0 +1,21 @@
+#pragma once
+
+/**
+ * tw::serial — umbrella include
+ *
+ * Include this single header to get the full serialisation API:
+ *   - BinaryBuffer  (backing store)
+ *   - BinaryWriter  (write cursor + Codec dispatch)
+ *   - BinaryReader  (read cursor + Codec dispatch)
+ *   - Codec<T>      (extensible type trait)
+ *   - Built-in Codec specialisations for all C++ primitive types
+ *   - GlmCodec      (vec2, vec3, vec4, mat4)
+ *   - EnttCodec     (entt::entity as uint32)
+ *   - WorldStateWriter / WorldStateReader  (game-specific high-level API)
+ */
+
+#include "BinaryBuffer.hpp"
+#include "Codec.hpp"
+#include "GlmCodec.hpp"
+#include "EnttCodec.hpp"
+#include "WorldStateWriter.hpp"

modules/serialization/include/tw/serial/WorldStateWriter.hpp

@@ -0,0 +1,261 @@
+#pragma once
+
+/**
+ * WorldStateWriter / WorldStateReader
+ * =====================================
+ * Project-specific serialisation for the per-frame world-state snapshot
+ * sent from the server to each connected client.
+ *
+ * Wire format (all values little-endian):
+ *
+ *   ┌──────────────────────────────────────────────────────────┐
+ *   │ Header (12 bytes)                                        │
+ *   │   packet_type  : uint32   (PacketType::WORLD_STATE = 3)  │
+ *   │   frame_idx    : uint32                                  │
+ *   │   entity_count : uint32   (number of position records)   │
+ *   ├──────────────────────────────────────────────────────────┤
+ *   │ Spawns section                                           │
+ *   │   spawn_count  : uint32                                  │
+ *   │   spawn[i].id  : uint32   × spawn_count                  │
+ *   ├──────────────────────────────────────────────────────────┤
+ *   │ Despawns section                                         │
+ *   │   despawn_count : uint32                                 │
+ *   │   despawn[i].id : uint32  × despawn_count                │
+ *   ├──────────────────────────────────────────────────────────┤
+ *   │ Entity positions (hot path — tightly packed)             │
+ *   │   [ id:uint32, x:float, y:float, z:float ] × entity_count│
+ *   └──────────────────────────────────────────────────────────┘
+ *
+ * Total minimum size : 20 bytes (header + empty spawns + empty despawns)
+ * Per entity         : 16 bytes
+ * 300 entities       : 20 + 300×16 = 4820 bytes  (well under MTU for segmented)
+ *
+ * Usage (server side, called once per client per frame):
+ *
+ *   tw::serial::WorldStateWriter w(buffer);      // buffer is a BinaryBuffer
+ *   w.begin(frame_idx);
+ *   w.write_spawns(interest.spawns());
+ *   w.write_despawns(interest.despawns());
+ *   w.begin_entities(num_entities);              // writes entity_count slot
+ *   for each entity in interest.entities():
+ *       w.write_entity(entity_id, position);
+ *   w.end();                                     // patches entity_count
+ *   // buffer.view() is ready to send
+ *
+ * Usage (client side):
+ *
+ *   tw::serial::WorldStateReader r(payload_span);
+ *   auto header = r.read_header();               // frame_idx + counts
+ *   for (auto id : r.read_spawns())   { ... }
+ *   for (auto id : r.read_despawns()) { ... }
+ *   while (r.has_entity()) {
+ *       auto [id, pos] = r.read_entity();
+ *       ...
+ *   }
+ */
+
+#include "Codec.hpp"
+#include "GlmCodec.hpp"
+#include "EnttCodec.hpp"
+
+#include <entt/entt.hpp>
+#include <glm/vec3.hpp>
+#include <cstdint>
+#include <span>
+#include <spdlog/spdlog.h>
+
+namespace tw::serial {
+
+// ── Packet type tag ───────────────────────────────────────────────────────
+// Mirrors PacketType::WORLD_STATE_PACKET (value 3) in packets/Packet.hpp.
+// Hardcoded here so the serialisation module does not depend on the network
+// module — the numerical value must stay in sync if the enum changes.
+inline constexpr uint32_t kWorldStatePacketType = 3; // WORLD_STATE_PACKET
+
+// ──────────────────────────────────────────────────────────────────────────
+// WorldStateWriter
+// ──────────────────────────────────────────────────────────────────────────
+
+class WorldStateWriter {
+    BinaryWriter  m_w;
+
+    // Offsets for length-prefix patching
+    std::size_t m_entity_count_offset{ 0 };
+    uint32_t    m_entity_count{ 0 };
+
+public:
+    explicit WorldStateWriter(BinaryBuffer& buf) noexcept : m_w(buf) {}
+
+    /**
+     * Write the packet header.  Call once per frame, before everything else.
+     * entity_count is patched in end().
+     */
+    void begin(uint32_t frame_idx) noexcept {
+        m_entity_count = 0;
+
+        // packet_type — lets the receiver dispatch without peeking further
+        m_w.encode<uint32_t>(kWorldStatePacketType);
+
+        // frame_idx
+        m_w.encode<uint32_t>(frame_idx);
+
+        // entity_count placeholder — patched when end() is called
+        m_entity_count_offset = m_w.reserve_u32();
+    }
+
+    // ── Spawns ────────────────────────────────────────────────────────────
+
+    /**
+     * Write the spawn list.  Pass any range of entt::entity.
+     */
+    template<typename Range>
+    void write_spawns(const Range& spawns) noexcept {
+        auto count = static_cast<uint32_t>(std::size(spawns));
+        m_w.encode<uint32_t>(count);
+        for (const entt::entity e : spawns) {
+            m_w.encode<entt::entity>(e);
+        }
+    }
+
+    // ── Despawns ──────────────────────────────────────────────────────────
+
+    template<typename Range>
+    void write_despawns(const Range& despawns) noexcept {
+        auto count = static_cast<uint32_t>(std::size(despawns));
+        // m_w.encode<uint32_t>(count);
+        for (const entt::entity e : despawns) {
+            m_w.encode<entt::entity>(e);
+        }
+    }
+
+    // ── Entity positions (the hot path) ───────────────────────────────────
+
+    /**
+     * Write a single entity position record.
+     * id  : raw uint32 of the entity handle
+     * pos : world-space position (x, y, z)
+     *
+     * This is the innermost loop of the replicator — every byte matters.
+     * The compiler will inline both calls down to two contiguous memcpys.
+     */
+    void write_entity(uint32_t id, const glm::vec3& pos) noexcept {
+        m_w.write(id);
+        // Write x, y, z as 3 contiguous floats
+        m_w.write_bytes(&pos.x, 3 * sizeof(float));
+        ++m_entity_count;
+    }
+
+    // Convenience overload accepting an entt::entity handle directly
+    void write_entity(entt::entity entity, const glm::vec3& pos) noexcept {
+        write_entity(static_cast<uint32_t>(entity), pos);
+    }
+
+    /**
+     * Patch the entity_count field written in begin() and finalise the
+     * buffer.  Must be called exactly once after all write_entity() calls.
+     */
+    void end() noexcept {
+        m_w.patch_u32(m_entity_count_offset, m_entity_count);
+    }
+
+    /** Expose the underlying buffer view (e.g. to pass to send_message). */
+    std::span<const std::byte> view() noexcept {
+        return m_w.buffer().view();
+    }
+
+    void reset() noexcept {
+        m_w.reset();
+        m_entity_count = 0;
+    }
+};
+
+// ──────────────────────────────────────────────────────────────────────────
+// WorldStateReader  (client-side / test use)
+// ──────────────────────────────────────────────────────────────────────────
+
+struct WorldStateHeader {
+    uint32_t packet_type;
+    uint32_t frame_idx;
+    uint32_t entity_count;
+};
+
+struct EntityRecord {
+    uint32_t  id;
+    glm::vec3 position;
+};
+
+class WorldStateReader {
+    BinaryReader m_r;
+    WorldStateHeader m_header{};
+
+    uint32_t m_spawn_count{ 0 };
+    uint32_t m_spawns_read{ 0 };
+
+    uint32_t m_despawn_count{ 0 };
+    uint32_t m_despawns_read{ 0 };
+
+    uint32_t m_entities_read{ 0 };
+
+public:
+    explicit WorldStateReader(std::span<const std::byte> data) noexcept
+        : m_r(data) {}
+
+    /** Read the 12-byte header. Must be called first. */
+    WorldStateHeader read_header() noexcept {
+        // m_header.packet_type  = m_r.decode<uint32_t>();
+        m_header.frame_idx    = m_r.decode<uint32_t>();
+        m_header.entity_count = m_r.decode<uint32_t>();
+
+        // spawn count follows immediately
+        m_spawn_count  = m_r.decode<uint32_t>();
+        return m_header;
+    }
+
+    /** Read the next spawn entity id.  Returns 0 when exhausted. */
+    bool has_spawn() const noexcept { return m_spawns_read < m_spawn_count; }
+
+    uint32_t read_spawn() noexcept {
+        assert(has_spawn());
+        ++m_spawns_read;
+        uint32_t id = m_r.decode<uint32_t>();
+        // if (!has_spawn()) {
+        //     // transition to despawns
+        //     m_despawn_count = m_r.decode<uint32_t>();
+        //     m_phase = Phase::Despawns;
+        // }
+        return id;
+    }
+
+    /** Skip remaining spawns and enter despawn phase. */
+    void skip_spawns() noexcept {
+        while (has_spawn()) read_spawn();
+    }
+
+    bool has_despawn() const noexcept { return m_despawns_read < m_despawn_count; }
+
+    uint32_t read_despawn() noexcept {
+        assert(has_despawn());
+        ++m_despawns_read;
+        uint32_t id = m_r.decode<uint32_t>();
+        return id;
+    }
+
+    void skip_despawns() noexcept {
+        while (has_despawn()) read_despawn();
+    }
+
+    bool has_entity() const noexcept {
+        return m_entities_read < m_header.entity_count;
+    }
+
+    EntityRecord read_entity() noexcept {
+        assert(has_entity());
+        EntityRecord rec;
+        rec.id = m_r.read<uint32_t>();
+        m_r.read_bytes(&rec.position.x, 3 * sizeof(float));
+        ++m_entities_read;
+        return rec;
+    }
+};
+
+} // namespace tw::serial