switch to xmake for package management (#611)

This change removes our dependency on vcpkg for package management, in favour of bringing some code in-tree in the `thirdparty` folder as well as using the xmake build-in package management feature. For the latter, all the package definitions are maintained in the zen repo itself, in the `repo` folder.

It should now also be easier to build the project as it will no longer depend on having the right version of vcpkg installed, which has been a common problem for new people coming in to the codebase. Now you should only need xmake to build.

* Bumps xmake requirement on github runners to 2.9.9 to resolve an issue where xmake on Windows invokes cmake with `v144` toolchain which does not exist
* BLAKE3 is now in-tree at `thirdparty/blake3`
* cpr is now in-tree at `thirdparty/cpr`
* cxxopts is now in-tree at `thirdparty/cxxopts`
* fmt is now in-tree at `thirdparty/fmt`
* robin-map is now in-tree at `thirdparty/robin-map`
* ryml is now in-tree at `thirdparty/ryml`
* sol2 is now in-tree at `thirdparty/sol2`
* spdlog is now in-tree at `thirdparty/spdlog`
* utfcpp is now in-tree at `thirdparty/utfcpp`
* xmake package repo definitions is in `repo`
* implemented support for sanitizers. ASAN is supported on windows, TSAN, UBSAN, MSAN etc are supported on Linux/MacOS though I have not yet tested it extensively on MacOS
* the zencore encryption implementation also now supports using mbedTLS which is used on MacOS, though for now we still use openssl on Linux
* crashpad
* bumps libcurl to 8.11.0 (from 8.8.0) which should address a rare build upload bug

4 files changed, 739 insertions, 0 deletions

diff --git a/thirdparty/ryml/src/c4/yml/detail/checks.hpp b/thirdparty/ryml/src/c4/yml/detail/checks.hpp
new file mode 100644
index 000000000..39b49e856
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/detail/checks.hpp
@@ -0,0 +1,200 @@
+#ifndef C4_YML_DETAIL_CHECKS_HPP_
+#define C4_YML_DETAIL_CHECKS_HPP_
+
+#include "c4/yml/tree.hpp"
+
+#ifdef __clang__
+#   pragma clang diagnostic push
+#elif defined(__GNUC__)
+#   pragma GCC diagnostic push
+#   pragma GCC diagnostic ignored "-Wtype-limits" // error: comparison of unsigned expression >= 0 is always true
+#elif defined(_MSC_VER)
+#   pragma warning(push)
+#   pragma warning(disable: 4296/*expression is always 'boolean_value'*/)
+#endif
+
+namespace c4 {
+namespace yml {
+
+
+void check_invariants(Tree const& t, size_t node=NONE);
+void check_free_list(Tree const& t);
+void check_arena(Tree const& t);
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+inline void check_invariants(Tree const& t, size_t node)
+{
+    if(node == NONE)
+    {
+        if(t.size() == 0) return;
+        node = t.root_id();
+    }
+
+    auto const& n = *t._p(node);
+#ifdef RYML_DBG
+    if(n.m_first_child != NONE || n.m_last_child != NONE)
+    {
+        printf("check(%zu): fc=%zu lc=%zu\n", node, n.m_first_child, n.m_last_child);
+    }
+    else
+    {
+        printf("check(%zu)\n", node);
+    }
+#endif
+
+    C4_CHECK(n.m_parent != node);
+    if(n.m_parent == NONE)
+    {
+        C4_CHECK(t.is_root(node));
+    }
+    else //if(n.m_parent != NONE)
+    {
+        C4_CHECK(t.has_child(n.m_parent, node));
+
+        auto const& p = *t._p(n.m_parent);
+        if(n.m_prev_sibling == NONE)
+        {
+            C4_CHECK(p.m_first_child == node);
+            C4_CHECK(t.first_sibling(node) == node);
+        }
+        else
+        {
+            C4_CHECK(p.m_first_child != node);
+            C4_CHECK(t.first_sibling(node) != node);
+        }
+
+        if(n.m_next_sibling == NONE)
+        {
+            C4_CHECK(p.m_last_child == node);
+            C4_CHECK(t.last_sibling(node) == node);
+        }
+        else
+        {
+            C4_CHECK(p.m_last_child != node);
+            C4_CHECK(t.last_sibling(node) != node);
+        }
+    }
+
+    C4_CHECK(n.m_first_child != node);
+    C4_CHECK(n.m_last_child != node);
+    if(n.m_first_child != NONE || n.m_last_child != NONE)
+    {
+        C4_CHECK(n.m_first_child != NONE);
+        C4_CHECK(n.m_last_child != NONE);
+    }
+
+    C4_CHECK(n.m_prev_sibling != node);
+    C4_CHECK(n.m_next_sibling != node);
+    if(n.m_prev_sibling != NONE)
+    {
+        C4_CHECK(t._p(n.m_prev_sibling)->m_next_sibling == node);
+        C4_CHECK(t._p(n.m_prev_sibling)->m_prev_sibling != node);
+    }
+    if(n.m_next_sibling != NONE)
+    {
+        C4_CHECK(t._p(n.m_next_sibling)->m_prev_sibling == node);
+        C4_CHECK(t._p(n.m_next_sibling)->m_next_sibling != node);
+    }
+
+    size_t count = 0;
+    for(size_t i = n.m_first_child; i != NONE; i = t.next_sibling(i))
+    {
+#ifdef RYML_DBG
+        printf("check(%zu):               descend to child[%zu]=%zu\n", node, count, i);
+#endif
+        auto const& ch = *t._p(i);
+        C4_CHECK(ch.m_parent == node);
+        C4_CHECK(ch.m_next_sibling != i);
+        ++count;
+    }
+    C4_CHECK(count == t.num_children(node));
+
+    if(n.m_prev_sibling == NONE && n.m_next_sibling == NONE)
+    {
+        if(n.m_parent != NONE)
+        {
+            C4_CHECK(t.num_children(n.m_parent) == 1);
+            C4_CHECK(t.num_siblings(node) == 1);
+        }
+    }
+
+    if(node == t.root_id())
+    {
+        C4_CHECK(t.size() == t.m_size);
+        C4_CHECK(t.capacity() == t.m_cap);
+        C4_CHECK(t.m_cap == t.m_size + t.slack());
+        check_free_list(t);
+        check_arena(t);
+    }
+
+    for(size_t i = t.first_child(node); i != NONE; i = t.next_sibling(i))
+    {
+        check_invariants(t, i);
+    }
+}
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+inline void check_free_list(Tree const& t)
+{
+    if(t.m_free_head == NONE)
+    {
+        C4_CHECK(t.m_free_tail == t.m_free_head);
+        return;
+    }
+
+    C4_CHECK(t.m_free_head >= 0 && t.m_free_head < t.m_cap);
+    C4_CHECK(t.m_free_tail >= 0 && t.m_free_tail < t.m_cap);
+
+    auto const& head = *t._p(t.m_free_head);
+    //auto const& tail = *t._p(t.m_free_tail);
+
+    //C4_CHECK(head.m_prev_sibling == NONE);
+    //C4_CHECK(tail.m_next_sibling == NONE);
+
+    size_t count = 0;
+    for(size_t i = t.m_free_head, prev = NONE; i != NONE; i = t._p(i)->m_next_sibling)
+    {
+        auto const& elm = *t._p(i);
+        if(&elm != &head)
+        {
+            C4_CHECK(elm.m_prev_sibling == prev);
+        }
+        prev = i;
+        ++count;
+    }
+    C4_CHECK(count == t.slack());
+}
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+inline void check_arena(Tree const& t)
+{
+    C4_CHECK(t.m_arena.len == 0 || (t.m_arena_pos >= 0 && t.m_arena_pos <= t.m_arena.len));
+    C4_CHECK(t.arena_size() == t.m_arena_pos);
+    C4_CHECK(t.arena_slack() + t.m_arena_pos == t.m_arena.len);
+}
+
+
+} /* namespace yml */
+} /* namespace c4 */
+
+#ifdef __clang__
+#   pragma clang diagnostic pop
+#elif defined(__GNUC__)
+#   pragma GCC diagnostic pop
+#elif defined(_MSC_VER)
+#   pragma warning(pop)
+#endif
+
+#endif /* C4_YML_DETAIL_CHECKS_HPP_ */
diff --git a/thirdparty/ryml/src/c4/yml/detail/parser_dbg.hpp b/thirdparty/ryml/src/c4/yml/detail/parser_dbg.hpp
new file mode 100644
index 000000000..457f1700d
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/detail/parser_dbg.hpp
@@ -0,0 +1,137 @@
+#ifndef _C4_YML_DETAIL_PARSER_DBG_HPP_
+#define _C4_YML_DETAIL_PARSER_DBG_HPP_
+
+#ifndef _C4_YML_COMMON_HPP_
+#include "../common.hpp"
+#endif
+#include <cstdio>
+
+//-----------------------------------------------------------------------------
+// some debugging scaffolds
+
+#if defined(_MSC_VER)
+#   pragma warning(push)
+#   pragma warning(disable: 4068/*unknown pragma*/)
+#endif
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wunknown-pragmas"
+//#pragma GCC diagnostic ignored "-Wpragma-system-header-outside-header"
+#pragma GCC system_header
+
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Werror"
+#pragma clang diagnostic ignored "-Wgnu-zero-variadic-macro-arguments"
+
+// some debugging scaffolds
+#ifdef RYML_DBG
+#include <c4/dump.hpp>
+namespace c4 {
+inline void _dbg_dumper(csubstr s) { fwrite(s.str, 1, s.len, stdout); };
+template<class ...Args>
+void _dbg_printf(c4::csubstr fmt, Args&& ...args)
+{
+    static char writebuf[256];
+    auto results = c4::format_dump_resume<&_dbg_dumper>(writebuf, fmt, std::forward<Args>(args)...);
+    // resume writing if the results failed to fit the buffer
+    if(C4_UNLIKELY(results.bufsize > sizeof(writebuf))) // bufsize will be that of the largest element serialized. Eg int(1), will require 1 byte.
+    {
+        results = format_dump_resume<&_dbg_dumper>(results, writebuf, fmt, std::forward<Args>(args)...);
+        if(C4_UNLIKELY(results.bufsize > sizeof(writebuf)))
+        {
+            results = format_dump_resume<&_dbg_dumper>(results, writebuf, fmt, std::forward<Args>(args)...);
+        }
+    }
+}
+} // namespace c4
+
+#   define _c4dbgt(fmt, ...)   this->_dbg ("{}:{}: "   fmt     , __FILE__, __LINE__, ## __VA_ARGS__)
+#   define _c4dbgpf(fmt, ...)  _dbg_printf("{}:{}: "   fmt "\n", __FILE__, __LINE__, ## __VA_ARGS__)
+#   define _c4dbgp(msg)        _dbg_printf("{}:{}: "   msg "\n", __FILE__, __LINE__                )
+#   define _c4dbgq(msg)        _dbg_printf(msg "\n")
+#   define _c4err(fmt, ...)   \
+    do { if(c4::is_debugger_attached()) { C4_DEBUG_BREAK(); } \
+         this->_err("ERROR:\n" "{}:{}: " fmt, __FILE__, __LINE__, ## __VA_ARGS__); } while(0)
+#else
+#   define _c4dbgt(fmt, ...)
+#   define _c4dbgpf(fmt, ...)
+#   define _c4dbgp(msg)
+#   define _c4dbgq(msg)
+#   define _c4err(fmt, ...)   \
+    do { if(c4::is_debugger_attached()) { C4_DEBUG_BREAK(); } \
+         this->_err("ERROR: " fmt, ## __VA_ARGS__); } while(0)
+#endif
+
+#define _c4prsp(sp) sp
+#define _c4presc(s) __c4presc(s.str, s.len)
+inline c4::csubstr _c4prc(const char &C4_RESTRICT c)
+{
+    switch(c)
+    {
+    case '\n': return c4::csubstr("\\n");
+    case '\t': return c4::csubstr("\\t");
+    case '\0': return c4::csubstr("\\0");
+    case '\r': return c4::csubstr("\\r");
+    case '\f': return c4::csubstr("\\f");
+    case '\b': return c4::csubstr("\\b");
+    case '\v': return c4::csubstr("\\v");
+    case '\a': return c4::csubstr("\\a");
+    default: return c4::csubstr(&c, 1);
+    }
+}
+inline void __c4presc(const char *s, size_t len)
+{
+    size_t prev = 0;
+    for(size_t i = 0; i < len; ++i)
+    {
+        switch(s[i])
+        {
+        case '\n'  : fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('n'); putchar('\n'); prev = i+1; break;
+        case '\t'  : fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('t'); prev = i+1; break;
+        case '\0'  : fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('0'); prev = i+1; break;
+        case '\r'  : fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('r'); prev = i+1; break;
+        case '\f'  : fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('f'); prev = i+1; break;
+        case '\b'  : fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('b'); prev = i+1; break;
+        case '\v'  : fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('v'); prev = i+1; break;
+        case '\a'  : fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('a'); prev = i+1; break;
+        case '\x1b': fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('e'); prev = i+1; break;
+        case -0x3e/*0xc2u*/:
+            if(i+1 < len)
+            {
+                if(s[i+1] == -0x60/*0xa0u*/)
+                {
+                    fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('_'); prev = i+2; ++i;
+                }
+                else if(s[i+1] == -0x7b/*0x85u*/)
+                {
+                    fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('N'); prev = i+2; ++i;
+                }
+                break;
+            }
+        case -0x1e/*0xe2u*/:
+            if(i+2 < len && s[i+1] == -0x80/*0x80u*/)
+            {
+                if(s[i+2] == -0x58/*0xa8u*/)
+                {
+                    fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('L'); prev = i+3; i += 2;
+                }
+                else if(s[i+2] == -0x57/*0xa9u*/)
+                {
+                    fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('P'); prev = i+3; i += 2;
+                }
+                break;
+            }
+        }
+    }
+    fwrite(s + prev, 1, len - prev, stdout);
+}
+
+#pragma clang diagnostic pop
+#pragma GCC diagnostic pop
+
+#if defined(_MSC_VER)
+#   pragma warning(pop)
+#endif
+
+
+#endif /* _C4_YML_DETAIL_PARSER_DBG_HPP_ */
diff --git a/thirdparty/ryml/src/c4/yml/detail/print.hpp b/thirdparty/ryml/src/c4/yml/detail/print.hpp
new file mode 100644
index 000000000..f88dc251d
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/detail/print.hpp
@@ -0,0 +1,128 @@
+#ifndef C4_YML_DETAIL_PRINT_HPP_
+#define C4_YML_DETAIL_PRINT_HPP_
+
+#include "c4/yml/tree.hpp"
+#include "c4/yml/node.hpp"
+
+
+namespace c4 {
+namespace yml {
+
+
+inline size_t print_node(Tree const& p, size_t node, int level, size_t count, bool print_children)
+{
+    printf("[%zd]%*s[%zd] %p", count, (2*level), "", node, (void*)p.get(node));
+    if(p.is_root(node))
+    {
+        printf(" [ROOT]");
+    }
+    printf(" %s:", p.type_str(node));
+    if(p.has_key(node))
+    {
+        if(p.has_key_anchor(node))
+        {
+            csubstr ka = p.key_anchor(node);
+            printf(" &%.*s", (int)ka.len, ka.str);
+        }
+        if(p.has_key_tag(node))
+        {
+            csubstr kt = p.key_tag(node);
+            csubstr k  = p.key(node);
+            printf(" %.*s '%.*s'", (int)kt.len, kt.str, (int)k.len, k.str);
+        }
+        else
+        {
+            csubstr k  = p.key(node);
+            printf(" '%.*s'", (int)k.len, k.str);
+        }
+    }
+    else
+    {
+        RYML_ASSERT( ! p.has_key_tag(node));
+    }
+    if(p.has_val(node))
+    {
+        if(p.has_val_tag(node))
+        {
+            csubstr vt = p.val_tag(node);
+            csubstr v  = p.val(node);
+            printf(" %.*s '%.*s'", (int)vt.len, vt.str, (int)v.len, v.str);
+        }
+        else
+        {
+            csubstr v  = p.val(node);
+            printf(" '%.*s'", (int)v.len, v.str);
+        }
+    }
+    else
+    {
+        if(p.has_val_tag(node))
+        {
+            csubstr vt = p.val_tag(node);
+            printf(" %.*s", (int)vt.len, vt.str);
+        }
+    }
+    if(p.has_val_anchor(node))
+    {
+        auto &a = p.val_anchor(node);
+        printf(" valanchor='&%.*s'", (int)a.len, a.str);
+    }
+    printf(" (%zd sibs)", p.num_siblings(node));
+
+    ++count;
+
+    if(p.is_container(node))
+    {
+        printf(" %zd children:\n", p.num_children(node));
+        if(print_children)
+        {
+            for(size_t i = p.first_child(node); i != NONE; i = p.next_sibling(i))
+            {
+                count = print_node(p, i, level+1, count, print_children);
+            }
+        }
+    }
+    else
+    {
+        printf("\n");
+    }
+
+    return count;
+}
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+inline void print_node(ConstNodeRef const& p, int level=0)
+{
+    print_node(*p.tree(), p.id(), level, 0, true);
+}
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+inline size_t print_tree(Tree const& p, size_t node=NONE)
+{
+    printf("--------------------------------------\n");
+    size_t ret = 0;
+    if(!p.empty())
+    {
+        if(node == NONE)
+            node = p.root_id();
+        ret = print_node(p, node, 0, 0, true);
+    }
+    printf("#nodes=%zd vs #printed=%zd\n", p.size(), ret);
+    printf("--------------------------------------\n");
+    return ret;
+}
+
+
+} /* namespace yml */
+} /* namespace c4 */
+
+
+#endif /* C4_YML_DETAIL_PRINT_HPP_ */
diff --git a/thirdparty/ryml/src/c4/yml/detail/stack.hpp b/thirdparty/ryml/src/c4/yml/detail/stack.hpp
new file mode 100644
index 000000000..95677ae27
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/detail/stack.hpp
@@ -0,0 +1,274 @@
+#ifndef _C4_YML_DETAIL_STACK_HPP_
+#define _C4_YML_DETAIL_STACK_HPP_
+
+#ifndef _C4_YML_COMMON_HPP_
+#include "../common.hpp"
+#endif
+
+#ifdef RYML_DBG
+#   include <type_traits>
+#endif
+
+#include <string.h>
+
+namespace c4 {
+namespace yml {
+namespace detail {
+
+/** A lightweight contiguous stack with SSO. This avoids a dependency on std. */
+template<class T, size_t N=16>
+class stack
+{
+    static_assert(std::is_trivially_copyable<T>::value, "T must be trivially copyable");
+    static_assert(std::is_trivially_destructible<T>::value, "T must be trivially destructible");
+
+    enum : size_t { sso_size = N };
+
+public:
+
+    T         m_buf[N];
+    T *       m_stack;
+    size_t    m_size;
+    size_t    m_capacity;
+    Callbacks m_callbacks;
+
+public:
+
+    constexpr static bool is_contiguous() { return true; }
+
+    stack(Callbacks const& cb)
+        : m_buf()
+        , m_stack(m_buf)
+        , m_size(0)
+        , m_capacity(N)
+        , m_callbacks(cb) {}
+    stack() : stack(get_callbacks()) {}
+    ~stack()
+    {
+        _free();
+    }
+
+    stack(stack const& that) noexcept : stack(that.m_callbacks)
+    {
+        resize(that.m_size);
+        _cp(&that);
+    }
+
+    stack(stack &&that) noexcept : stack(that.m_callbacks)
+    {
+        _mv(&that);
+    }
+
+    stack& operator= (stack const& that) noexcept
+    {
+        _cb(that.m_callbacks);
+        resize(that.m_size);
+        _cp(&that);
+        return *this;
+    }
+
+    stack& operator= (stack &&that) noexcept
+    {
+        _cb(that.m_callbacks);
+        _mv(&that);
+        return *this;
+    }
+
+public:
+
+    size_t size() const { return m_size; }
+    size_t empty() const { return m_size == 0; }
+    size_t capacity() const { return m_capacity; }
+
+    void clear()
+    {
+        m_size = 0;
+    }
+
+    void resize(size_t sz)
+    {
+        reserve(sz);
+        m_size = sz;
+    }
+
+    void reserve(size_t sz);
+
+    void push(T const& C4_RESTRICT n)
+    {
+        RYML_ASSERT((const char*)&n + sizeof(T) < (const char*)m_stack || &n > m_stack + m_capacity);
+        if(m_size == m_capacity)
+        {
+            size_t cap = m_capacity == 0 ? N : 2 * m_capacity;
+            reserve(cap);
+        }
+        m_stack[m_size] = n;
+        ++m_size;
+    }
+
+    void push_top()
+    {
+        RYML_ASSERT(m_size > 0);
+        if(m_size == m_capacity)
+        {
+            size_t cap = m_capacity == 0 ? N : 2 * m_capacity;
+            reserve(cap);
+        }
+        m_stack[m_size] = m_stack[m_size - 1];
+        ++m_size;
+    }
+
+    T const& C4_RESTRICT pop()
+    {
+        RYML_ASSERT(m_size > 0);
+        --m_size;
+        return m_stack[m_size];
+    }
+
+    C4_ALWAYS_INLINE T const& C4_RESTRICT top() const { RYML_ASSERT(m_size > 0); return m_stack[m_size - 1]; }
+    C4_ALWAYS_INLINE T      & C4_RESTRICT top()       { RYML_ASSERT(m_size > 0); return m_stack[m_size - 1]; }
+
+    C4_ALWAYS_INLINE T const& C4_RESTRICT bottom() const { RYML_ASSERT(m_size > 0); return m_stack[0]; }
+    C4_ALWAYS_INLINE T      & C4_RESTRICT bottom()       { RYML_ASSERT(m_size > 0); return m_stack[0]; }
+
+    C4_ALWAYS_INLINE T const& C4_RESTRICT top(size_t i) const { RYML_ASSERT(i < m_size); return m_stack[m_size - 1 - i]; }
+    C4_ALWAYS_INLINE T      & C4_RESTRICT top(size_t i)       { RYML_ASSERT(i < m_size); return m_stack[m_size - 1 - i]; }
+
+    C4_ALWAYS_INLINE T const& C4_RESTRICT bottom(size_t i) const { RYML_ASSERT(i < m_size); return m_stack[i]; }
+    C4_ALWAYS_INLINE T      & C4_RESTRICT bottom(size_t i)       { RYML_ASSERT(i < m_size); return m_stack[i]; }
+
+    C4_ALWAYS_INLINE T const& C4_RESTRICT operator[](size_t i) const { RYML_ASSERT(i < m_size); return m_stack[i]; }
+    C4_ALWAYS_INLINE T      & C4_RESTRICT operator[](size_t i)       { RYML_ASSERT(i < m_size); return m_stack[i]; }
+
+public:
+
+    using       iterator = T       *;
+    using const_iterator = T const *;
+
+    iterator begin() { return m_stack; }
+    iterator end  () { return m_stack + m_size; }
+
+    const_iterator begin() const { return (const_iterator)m_stack; }
+    const_iterator end  () const { return (const_iterator)m_stack + m_size; }
+
+public:
+    void _free();
+    void _cp(stack const* C4_RESTRICT that);
+    void _mv(stack * that);
+    void _cb(Callbacks const& cb);
+};
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+template<class T, size_t N>
+void stack<T, N>::reserve(size_t sz)
+{
+    if(sz <= m_size)
+        return;
+    if(sz <= N)
+    {
+        m_stack = m_buf;
+        m_capacity = N;
+        return;
+    }
+    T *buf = (T*) m_callbacks.m_allocate(sz * sizeof(T), m_stack, m_callbacks.m_user_data);
+    memcpy(buf, m_stack, m_size * sizeof(T));
+    if(m_stack != m_buf)
+    {
+        m_callbacks.m_free(m_stack, m_capacity * sizeof(T), m_callbacks.m_user_data);
+    }
+    m_stack = buf;
+    m_capacity = sz;
+}
+
+
+//-----------------------------------------------------------------------------
+
+template<class T, size_t N>
+void stack<T, N>::_free()
+{
+    RYML_ASSERT(m_stack != nullptr); // this structure cannot be memset() to zero
+    if(m_stack != m_buf)
+    {
+        m_callbacks.m_free(m_stack, m_capacity * sizeof(T), m_callbacks.m_user_data);
+        m_stack = m_buf;
+        m_size = N;
+        m_capacity = N;
+    }
+    else
+    {
+        RYML_ASSERT(m_capacity == N);
+    }
+}
+
+
+//-----------------------------------------------------------------------------
+
+template<class T, size_t N>
+void stack<T, N>::_cp(stack const* C4_RESTRICT that)
+{
+    if(that->m_stack != that->m_buf)
+    {
+        RYML_ASSERT(that->m_capacity > N);
+        RYML_ASSERT(that->m_size <= that->m_capacity);
+    }
+    else
+    {
+        RYML_ASSERT(that->m_capacity <= N);
+        RYML_ASSERT(that->m_size <= that->m_capacity);
+    }
+    memcpy(m_stack, that->m_stack, that->m_size * sizeof(T));
+    m_size = that->m_size;
+    m_capacity = that->m_size < N ? N : that->m_size;
+    m_callbacks = that->m_callbacks;
+}
+
+
+//-----------------------------------------------------------------------------
+
+template<class T, size_t N>
+void stack<T, N>::_mv(stack * that)
+{
+    if(that->m_stack != that->m_buf)
+    {
+        RYML_ASSERT(that->m_capacity > N);
+        RYML_ASSERT(that->m_size <= that->m_capacity);
+        m_stack = that->m_stack;
+    }
+    else
+    {
+        RYML_ASSERT(that->m_capacity <= N);
+        RYML_ASSERT(that->m_size <= that->m_capacity);
+        memcpy(m_buf, that->m_buf, that->m_size * sizeof(T));
+        m_stack = m_buf;
+    }
+    m_size = that->m_size;
+    m_capacity = that->m_capacity;
+    m_callbacks = that->m_callbacks;
+    // make sure no deallocation happens on destruction
+    RYML_ASSERT(that->m_stack != m_buf);
+    that->m_stack = that->m_buf;
+    that->m_capacity = N;
+    that->m_size = 0;
+}
+
+
+//-----------------------------------------------------------------------------
+
+template<class T, size_t N>
+void stack<T, N>::_cb(Callbacks const& cb)
+{
+    if(cb != m_callbacks)
+    {
+        _free();
+        m_callbacks = cb;
+    }
+}
+
+} // namespace detail
+} // namespace yml
+} // namespace c4
+
+#endif /* _C4_YML_DETAIL_STACK_HPP_ */