v4.2.1

First steps for compile-time and run-time JMESPath query support

v4.2.0 neutered the partial_read option, due to its complexity and confusing behavior (and to make it faster). This release brings another approach to partial reading that is far more extensible, by utilizing the JMESPath query specification.

More JMESPath support will be added in the future, but this release brings both compile-time and run-time JMESPath expression handling to read a value at a target location in a buffer.

Example

struct Person
{
   std::string first_name{};
   std::string last_name{};
   uint16_t age{};
};

struct Family
{
   Person father{};
   Person mother{};
   std::vector<Person> children{};
};

struct Home
{
   Family family{};
   std::string address{};
};

suite jmespath_read_at_tests = [] {
   "compile-time read_jmespath"_test = [] {
      Home home{.family = {.father = {"Gilbert", "Fox", 28},
                           .mother = {"Anne", "Fox", 30},
                           .children = {{"Lilly"}, {"Vincent"}}}};

      std::string buffer{};
      expect(not glz::write_json(home, buffer));

      std::string first_name{};
      auto ec = glz::read_jmespath<"family.father.first_name">(first_name, buffer);
      expect(not ec) << glz::format_error(ec, buffer);
      expect(first_name == "Gilbert");

      Person child{};
      expect(not glz::read_jmespath<"family.children[0]">(child, buffer));
      expect(child.first_name == "Lilly");
      expect(not glz::read_jmespath<"family.children[1]">(child, buffer));
      expect(child.first_name == "Vincent");
   };

   "run-time read_jmespath"_test = [] {
      Home home{.family = {.father = {"Gilbert", "Fox", 28},
                           .mother = {"Anne", "Fox", 30},
                           .children = {{"Lilly"}, {"Vincent"}}}};

      std::string buffer{};
      expect(not glz::write_json(home, buffer));

      std::string first_name{};
      auto ec = glz::read_jmespath("family.father.first_name", first_name, buffer);
      expect(not ec) << glz::format_error(ec, buffer);
      expect(first_name == "Gilbert");

      Person child{};
      expect(not glz::read_jmespath("family.children[0]", child, buffer));
      expect(child.first_name == "Lilly");
      expect(not glz::read_jmespath("family.children[1]", child, buffer));
      expect(child.first_name == "Vincent");
   };
};

by @stephenberry in #1509

Other Improvements

• allow subclassing json_t by @benine203 in #1504

Full Changelog: v4.2.0...v4.2.1