Improve behaviour of tree creation and Tree::root_id().

`Tree` is now non-empty by default, and `Tree::root_id()` will no longer modify the tree when it is empty. To create an empty tree now it is necessary to use the capacity constructor with a capacity of zero:
  ```c++
  // default-constructed tree is now non-empty
  Tree tree;
  assert(!tree.empty()); // MODIFIED! was empty on previous version
  id_type root = tree.root_id(); // OK. default-constructed tree is now non-empty

  // to create an empty tree:
  Tree tree(0); // pass capacity of zero
  assert(tree.empty()); // as expected
  // but watchout, this is no longer possible:
  //id_type root = tree.root_id(); // ERROR: cannot get root of empty tree.
  ```
This changeset also enables the python library to call `root_id()` on a default-constructed tree

re #556

Author: biojppm

api/python/tests/test_basic.py

@@ -0,0 +1,13 @@
+import ryml
+
+
+def test_create_empty_tree():
+    tree = ryml.Tree(0)
+    assert tree.empty()
+
+
+def test_create_tree():
+    tree = ryml.Tree()
+    assert not tree.empty()
+    root = tree.root_id()
+    tree.to_seq(root)

api/ryml.i

@@ -597,10 +597,11 @@ using id_type = RYML_ID_TYPE;
 struct Tree
 {
     Tree();
+    Tree(id_type node_type, size_t arena_capacity=RYML_DEFAULT_TREE_ARENA_CAPACITY);
     ~Tree();
 
-    void reserve(id_type node_capacity);
-    void reserve_arena(size_t arena_capacity);
+    void reserve(id_type node_capacity=RYML_DEFAULT_TREE_CAPACITY);
+    void reserve_arena(size_t arena_capacity=RYML_DEFAULT_TREE_ARENA_CAPACITY);
     void clear();
     void clear_arena();
 

changelog/current.md

@@ -6,3 +6,17 @@
   ---
   more data here
   ```
+- [PR#557](https://github.com/biojppm/rapidyaml/pull/557) - `Tree` is now non-empty by default, and `Tree::root_id()` will no longer modify the tree when it is empty. To create an empty tree now it is necessary to use the capacity constructor with a capacity of zero:
+  ```c++
+  // default-constructed tree is now non-empty
+  Tree tree;
+  assert(!tree.empty()); // MODIFIED! was empty on previous version
+  id_type root = tree.root_id(); // OK. default-constructed tree is now non-empty
+  
+  // to create an empty tree:
+  Tree tree(0); // pass capacity of zero
+  assert(tree.empty()); // as expected
+  // but watchout, this is no longer possible:
+  //id_type root = tree.root_id(); // ERROR: cannot get root of empty tree.
+  ```
+  This changeset also enables the python library to call `root_id()` on a default-constructed tree (fixes [#556](https://github.com/biojppm/rapidyaml/issues/556)).

samples/quickstart.cpp

@@ -3911,7 +3911,7 @@ void sample_float_precision()
     // have to build the container.
     //
     // First a function to check the result:
-    auto check_precision = [&](ryml::Tree serialized){
+    auto check_precision = [&](ryml::Tree const& serialized){
         std::cout << serialized;
         // now it works!
         CHECK((ryml::emitrs_yaml<std::string>(serialized) == R"(- 1.23234412342131239

src/c4/yml/common.hpp

@@ -22,6 +22,16 @@
 
 //-----------------------------------------------------------------------------
 
+#ifndef RYML_DEFAULT_TREE_CAPACITY
+/// default capacity for the tree when not set explicitly
+#define RYML_DEFAULT_TREE_CAPACITY (16)
+#endif
+
+#ifndef RYML_DEFAULT_TREE_ARENA_CAPACITY
+/// default capacity for the tree's arena when not set explicitly
+#define RYML_DEFAULT_TREE_ARENA_CAPACITY (0)
+#endif
+
 #ifndef RYML_ERRMSG_SIZE
 /// size for the error message buffer
 #define RYML_ERRMSG_SIZE (1024)

src/c4/yml/parse.cpp

@@ -10,6 +10,7 @@ C4_SUPPRESS_WARNING_GCC_CLANG_WITH_PUSH("-Wold-style-cast")
 C4_SUPPRESS_WARNING_GCC("-Wtype-limits")
 C4_SUPPRESS_WARNING_GCC("-Wuseless-cast")
 
+
 namespace c4 {
 namespace yml {
 
@@ -82,6 +83,11 @@ ConstNodeRef Tree::cdocref(id_type i) const
 
 //-----------------------------------------------------------------------------
 Tree::Tree(Callbacks const& cb)
+    : Tree(RYML_DEFAULT_TREE_CAPACITY, RYML_DEFAULT_TREE_ARENA_CAPACITY, cb)
+{
+}
+
+Tree::Tree(id_type node_capacity, size_t arena_capacity, Callbacks const& cb)
     : m_buf(nullptr)
     , m_cap(0)
     , m_size(0)
@@ -92,13 +98,10 @@ Tree::Tree(Callbacks const& cb)
     , m_callbacks(cb)
     , m_tag_directives()
 {
-}
-
-Tree::Tree(id_type node_capacity, size_t arena_capacity, Callbacks const& cb)
-    : Tree(cb)
-{
-    reserve(node_capacity);
-    reserve_arena(arena_capacity);
+    if(node_capacity)
+        reserve(node_capacity);
+    if(arena_capacity)
+        reserve_arena(arena_capacity);
 }
 
 Tree::~Tree()
@@ -107,11 +110,18 @@ Tree::~Tree()
 }
 
 
-Tree::Tree(Tree const& that) : Tree(that.m_callbacks)
+Tree::Tree(Tree const& that) : m_callbacks(that.m_callbacks)
 {
+    _clear();
     _copy(that);
 }
 
+Tree::Tree(Tree && that) noexcept : m_callbacks(that.m_callbacks)
+{
+    _clear();
+    _move(that);
+}
+
 Tree& Tree::operator= (Tree const& that)
 {
     if(&that != this)
@@ -123,11 +133,6 @@ Tree& Tree::operator= (Tree const& that)
     return *this;
 }
 
-Tree::Tree(Tree && that) noexcept : Tree(that.m_callbacks)
-{
-    _move(that);
-}
-
 Tree& Tree::operator= (Tree && that) noexcept
 {
     if(&that != this)

src/c4/yml/tree.cpp

@@ -33,7 +33,6 @@ C4_SUPPRESS_WARNING_GCC_CLANG("-Wold-style-cast")
 C4_SUPPRESS_WARNING_GCC("-Wuseless-cast")
 C4_SUPPRESS_WARNING_GCC("-Wtype-limits")
 
-
 namespace c4 {
 namespace yml {
 
@@ -206,7 +205,7 @@ class RYML_EXPORT Tree
 
     Tree() : Tree(get_callbacks()) {}
     Tree(Callbacks const& cb);
-    Tree(id_type node_capacity, size_t arena_capacity=0) : Tree(node_capacity, arena_capacity, get_callbacks()) {}
+    Tree(id_type node_capacity, size_t arena_capacity=RYML_DEFAULT_TREE_ARENA_CAPACITY) : Tree(node_capacity, arena_capacity, get_callbacks()) {}
     Tree(id_type node_capacity, size_t arena_capacity, Callbacks const& cb);
 
     ~Tree();
@@ -224,7 +223,7 @@ class RYML_EXPORT Tree
     /** @name memory and sizing */
     /** @{ */
 
-    void reserve(id_type node_capacity);
+    void reserve(id_type node_capacity=RYML_DEFAULT_TREE_CAPACITY);
 
     /** clear the tree and zero every node
      * @note does NOT clear the arena
@@ -284,10 +283,8 @@ class RYML_EXPORT Tree
     //! This function is implementation only; use at your own risk.
     NodeData const * _p(id_type node) const { _RYML_CB_ASSERT(m_callbacks, node != NONE && node >= 0 && node < m_cap); return m_buf + node; }
 
-    //! Get the id of the root node
-    id_type root_id()       { if(m_cap == 0) { reserve(16); } _RYML_CB_ASSERT(m_callbacks, m_cap > 0 && m_size > 0); return 0; }
-    //! Get the id of the root node
-    id_type root_id() const {                                 _RYML_CB_ASSERT(m_callbacks, m_cap > 0 && m_size > 0); return 0; }
+    //! Get the id of the root node. The tree must not be empty.
+    id_type root_id() const { _RYML_CB_ASSERT(m_callbacks, m_cap > 0 && m_size > 0); return 0; }
 
     //! Get a NodeRef of a node by id
     NodeRef      ref(id_type node);
@@ -313,17 +310,17 @@ class RYML_EXPORT Tree
     //! @note @p i is NOT the node id, but the doc position within the stream
     ConstNodeRef cdocref(id_type i) const;
 
-    //! find a root child by name, return it as a NodeRef
+    //! find a root child (ie child of root) by name, return it as a NodeRef
     //! @note requires the root to be a map.
     NodeRef      operator[] (csubstr key);
-    //! find a root child by name, return it as a NodeRef
+    //! find a root child (ie child of root) by name, return it as a NodeRef
     //! @note requires the root to be a map.
     ConstNodeRef operator[] (csubstr key) const;
 
-    //! find a root child by index: return the root node's @p i-th child as a NodeRef
+    //! find a root child (ie child of root) by index: return the root node's @p i-th child as a NodeRef
     //! @note @p i is NOT the node id, but the child's position
     NodeRef      operator[] (id_type i);
-    //! find a root child by index: return the root node's @p i-th child as a NodeRef
+    //! find a root child (ie child of root) by index: return the root node's @p i-th child as a NodeRef
     //! @note @p i is NOT the node id, but the child's position
     ConstNodeRef operator[] (id_type i) const;
 
@@ -971,7 +968,7 @@ class RYML_EXPORT Tree
      * @warning This operation may be expensive, with a potential complexity of O(numNodes)+O(arenasize).
      * @warning Growing the arena may cause relocation of the entire
      * existing arena, and thus change the contents of individual nodes. */
-    void reserve_arena(size_t arena_cap)
+    void reserve_arena(size_t arena_cap=RYML_DEFAULT_TREE_ARENA_CAPACITY)
     {
         if(arena_cap > m_arena.len)
         {

src/c4/yml/tree.hpp

@@ -492,7 +492,7 @@ TEST(CaseNode, anchors)
 
 TEST(simple_anchor, resolve_works_on_an_empty_tree)
 {
-    Tree t;
+    Tree t(0);
     t.resolve();
     EXPECT_TRUE(t.empty());
 }

test/test_anchor.cpp

@@ -310,7 +310,7 @@ struct CaseDataLineEndings
     std::vector<char> src_buf;
     substr src;
 
-    Tree parsed_tree;
+    Tree parsed_tree{0};
 
     size_t numbytes_stdout;
     size_t numbytes_stdout_json;
@@ -327,10 +327,10 @@ struct CaseDataLineEndings
     std::string parse_buf_json;
     substr parsed_json;
 
-    Tree emitted_tree;
-    Tree emitted_tree_json;
+    Tree emitted_tree{0};
+    Tree emitted_tree_json{0};
 
-    Tree recreated;
+    Tree recreated{0};
 
     std::string parse_buf_ints;
     std::vector<int> parsed_ints;