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Implement a new JSON::try_at with a start hint
Signed-off-by: Juan Cruz Viotti <jv@jviotti.com>
1 parent 1d572ae commit 01f1927

3 files changed

Lines changed: 178 additions & 0 deletions

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‎src/core/json/include/sourcemeta/core/json_object.h‎

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@@ -270,6 +270,35 @@ template <typename Key, typename Value, typename Hash> class JSONObject {
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return nullptr;
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}
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/// Try to access an object entry, scanning from a caller-provided start
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/// offset. On hit, advances `start` past the found index
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[[nodiscard]] inline auto try_at(const Key &key, const hash_type key_hash,
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size_type &start) const
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-> const mapped_type * {
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assert(this->hash(key) == key_hash);
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const auto object_size{this->size()};
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if (this->hasher.is_perfect(key_hash)) {
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for (size_type count = 0; count < object_size; count++) {
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const auto index{(start + count) % object_size};
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if (this->data[index].hash == key_hash) {
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start = index + 1;
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return &this->data[index].second;
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}
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}
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} else {
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for (size_type count = 0; count < object_size; count++) {
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const auto index{(start + count) % object_size};
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if (this->data[index].hash == key_hash &&
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this->data[index].first == key) {
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start = index + 1;
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return &this->data[index].second;
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}
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}
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}
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return nullptr;
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}
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/// Try to emplace a property before another property
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auto try_emplace_before(const Key &key, const mapped_type &value,
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const Key &suffix) -> hash_type {

‎src/core/json/include/sourcemeta/core/json_value.h‎

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@@ -1282,6 +1282,38 @@ class SOURCEMETA_CORE_JSON_EXPORT JSON {
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return object.try_at(key, hash);
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}
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/// Try to get a property, scanning from a caller-provided start offset.
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/// On hit, advances `start` past the found index. When looking up multiple
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/// keys in insertion order, each lookup hits on the first probe, making the
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/// total work O(N) instead of O(N^2). For example:
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///
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/// ```cpp
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/// #include <sourcemeta/core/json.h>
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/// #include <cassert>
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///
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/// const sourcemeta::core::JSON document =
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/// sourcemeta::core::parse_json("{ \"foo\": 1, \"bar\": 2 }");
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/// const auto &object{document.as_object()};
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/// typename decltype(object)::size_type start{0};
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///
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/// const auto hash_foo{object.hash("foo")};
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/// const auto *foo{document.try_at("foo", hash_foo, start)};
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/// assert(foo);
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/// assert(foo->to_integer() == 1);
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///
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/// const auto hash_bar{object.hash("bar")};
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/// const auto *bar{document.try_at("bar", hash_bar, start)};
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/// assert(bar);
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/// assert(bar->to_integer() == 2);
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/// ```
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[[nodiscard]] SOURCEMETA_FORCEINLINE inline auto
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try_at(const String &key, const typename Object::hash_type hash,
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typename Object::size_type &start) const -> const JSON * {
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assert(this->is_object());
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const auto &object{this->data_object};
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return object.try_at(key, hash, start);
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}
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/// This method checks whether an input JSON object defines a specific key.
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/// For example:
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///

‎test/json/json_object_test.cc‎

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Original file line numberDiff line numberDiff line change
@@ -1093,3 +1093,120 @@ TEST(JSON_object, reorder_already_ordered) {
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EXPECT_EQ(iterator->first, "cherry");
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EXPECT_EQ(iterator->second.to_integer(), 3);
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}
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TEST(JSON_object, try_at_start_hit) {
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const sourcemeta::core::JSON document =
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sourcemeta::core::parse_json("{\"foo\":1,\"bar\":2,\"baz\":3}");
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const auto &object{document.as_object()};
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sourcemeta::core::JSON::Object::size_type start{0};
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const auto hash_foo{object.hash("foo")};
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const auto *result_foo{object.try_at("foo", hash_foo, start)};
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EXPECT_TRUE(result_foo);
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EXPECT_EQ(result_foo->to_integer(), 1);
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EXPECT_EQ(start, 1);
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const auto hash_bar{object.hash("bar")};
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const auto *result_bar{object.try_at("bar", hash_bar, start)};
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EXPECT_TRUE(result_bar);
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EXPECT_EQ(result_bar->to_integer(), 2);
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EXPECT_EQ(start, 2);
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const auto hash_baz{object.hash("baz")};
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const auto *result_baz{object.try_at("baz", hash_baz, start)};
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EXPECT_TRUE(result_baz);
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EXPECT_EQ(result_baz->to_integer(), 3);
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EXPECT_EQ(start, 3);
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}
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TEST(JSON_object, try_at_start_miss) {
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const sourcemeta::core::JSON document =
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sourcemeta::core::parse_json("{\"foo\":1,\"bar\":2}");
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const auto &object{document.as_object()};
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sourcemeta::core::JSON::Object::size_type start{0};
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const auto hash_missing{object.hash("missing")};
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const auto *result{object.try_at("missing", hash_missing, start)};
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EXPECT_FALSE(result);
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EXPECT_EQ(start, 0);
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}
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TEST(JSON_object, try_at_start_reverse_order) {
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const sourcemeta::core::JSON document =
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sourcemeta::core::parse_json("{\"foo\":1,\"bar\":2,\"baz\":3}");
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const auto &object{document.as_object()};
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sourcemeta::core::JSON::Object::size_type start{0};
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const auto hash_baz{object.hash("baz")};
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const auto *result_baz{object.try_at("baz", hash_baz, start)};
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EXPECT_TRUE(result_baz);
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EXPECT_EQ(result_baz->to_integer(), 3);
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EXPECT_EQ(start, 3);
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const auto hash_bar{object.hash("bar")};
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const auto *result_bar{object.try_at("bar", hash_bar, start)};
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EXPECT_TRUE(result_bar);
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EXPECT_EQ(result_bar->to_integer(), 2);
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EXPECT_EQ(start, 2);
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const auto hash_foo{object.hash("foo")};
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const auto *result_foo{object.try_at("foo", hash_foo, start)};
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EXPECT_TRUE(result_foo);
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EXPECT_EQ(result_foo->to_integer(), 1);
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EXPECT_EQ(start, 1);
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}
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TEST(JSON_object, try_at_start_single_property) {
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const sourcemeta::core::JSON document =
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sourcemeta::core::parse_json("{\"only\":42}");
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const auto &object{document.as_object()};
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sourcemeta::core::JSON::Object::size_type start{0};
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const auto hash_only{object.hash("only")};
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const auto *result{object.try_at("only", hash_only, start)};
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EXPECT_TRUE(result);
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EXPECT_EQ(result->to_integer(), 42);
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EXPECT_EQ(start, 1);
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}
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TEST(JSON_object, try_at_start_wraparound) {
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const sourcemeta::core::JSON document =
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sourcemeta::core::parse_json("{\"foo\":1,\"bar\":2,\"baz\":3}");
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const auto &object{document.as_object()};
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sourcemeta::core::JSON::Object::size_type start{10};
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const auto hash_foo{object.hash("foo")};
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const auto *result{object.try_at("foo", hash_foo, start)};
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EXPECT_TRUE(result);
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EXPECT_EQ(result->to_integer(), 1);
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EXPECT_EQ(start, 1);
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}
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TEST(JSON_object, try_at_start_sequential_advances) {
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const sourcemeta::core::JSON document =
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sourcemeta::core::parse_json("{\"a\":1,\"b\":2,\"c\":3,\"d\":4}");
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const auto &object{document.as_object()};
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sourcemeta::core::JSON::Object::size_type start{0};
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const auto hash_a{object.hash("a")};
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const auto *result_a{object.try_at("a", hash_a, start)};
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EXPECT_TRUE(result_a);
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EXPECT_EQ(result_a->to_integer(), 1);
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const auto hash_b{object.hash("b")};
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const auto *result_b{object.try_at("b", hash_b, start)};
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EXPECT_TRUE(result_b);
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EXPECT_EQ(result_b->to_integer(), 2);
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const auto hash_c{object.hash("c")};
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const auto *result_c{object.try_at("c", hash_c, start)};
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EXPECT_TRUE(result_c);
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EXPECT_EQ(result_c->to_integer(), 3);
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const auto hash_d{object.hash("d")};
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const auto *result_d{object.try_at("d", hash_d, start)};
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EXPECT_TRUE(result_d);
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EXPECT_EQ(result_d->to_integer(), 4);
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EXPECT_EQ(start, object.size());
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}

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