initial implementation

CMakeLists.txt

@@ -0,0 +1,52 @@
+# printjson/CMakeLists.txt
+
+cmake_minimum_required(VERSION 3.10)
+
+project(printjson VERSION 0.1)
+enable_language(CXX)
+
+# common XO cmake macros (see proj/xo-cmake)
+include(xo_macros/xo_cxx)
+include(xo_macros/code-coverage)
+
+# ----------------------------------------------------------------
+# unit test setup
+
+enable_testing()
+# activate code coverage for all executables + libraries (when configured with -DCODE_COVERAGE=ON)
+add_code_coverage()
+# 1. assuming that /nix/store/ prefixes .hpp files belonging to gcc, catch2 etc.
+#    we're not interested in code coverage for these sources.
+# 2. exclude the utest/ subdir, we don't need coverage on the unit tests themselves;
+#    rather,  want coverage on the code that the unit tests exercise.
+#
+# NOTE: this seems to work only with the 'ccov-all' target.  In particular,  doesn't seem to do anything with the 'ccov' target
+#
+add_code_coverage_all_targets(EXCLUDE /nix/store/* ${PROJECT_SOURCE_DIR}/utest/* ${PROJECT_BINARY_DIR}/local/* ${PROJECT_SOURCE_DIR}/repo/*)
+
+# ----------------------------------------------------------------
+# c++ settings
+
+# one-time project-specific c++ flags.  usually empty
+set(PROJECT_CXX_FLAGS "")
+#set(PROJECT_CXX_FLAGS "-fconcepts-diagnostics-depth=2")
+add_definitions(${PROJECT_CXX_FLAGS})
+
+xo_toplevel_compile_options()
+
+# ----------------------------------------------------------------
+
+add_subdirectory(src/printjson)
+#add_subdirectory(utest)
+
+# ----------------------------------------------------------------
+# provide find_package() support for printjson customers
+
+xo_export_cmake_config(${PROJECT_NAME} ${PROJECT_VERSION} ${PROJECT_NAME}Targets)
+
+# ----------------------------------------------------------------
+# install .hpp files
+
+xo_install_include_tree()
+
+# end CMakeLists.txt

README.md

@@ -0,0 +1,26 @@
+# printjson library
+
+### build + install
+```
+$ cd xo-printjson
+$ mkdir build
+$ cd build
+$ PREFIX=/usr/local  # or wherever you prefer
+$ cmake -DCMAKE_MODULE_PATH=${PREFIX}/share/cmake -DCMAKE_PREFIX_PATH=${PREFIX} -DCMAKE_INSTALL_PREFIX=${PREFIX} ..
+$ make
+$ make install
+```
+
+### build for unit test coverage
+```
+$ cd xo-printjson
+$ mkdir ccov
+$ cd ccov
+$ cmake -DCMAKE_MODULE_PATH=${PREFIX}/share/cmake  -DCMAKE_PREFIX_PATH=${PREFIX} -DCODE_COVERAGE=ON -DCMAKE_BUILD_TYPE=Debug ..
+```
+
+### LSP support
+```
+$ cd xo-printjson
+$ ln -s build/compile_commands.json  # lsp will look for compile_commands.json in the root of the source tree
+```

cmake/printjsonConfig.cmake.in

@@ -0,0 +1,6 @@
+@PACKAGE_INIT@
+
+#include(CMakeFindDependencyMacro)
+#find_dependency(refcnt)
+include("${CMAKE_CURRENT_LIST_DIR}/@PROJECT_NAME@Targets.cmake")
+check_required_components("@PROJECT_NAME@")

include/xo/printjson/JsonPrinter.hpp

@@ -0,0 +1,99 @@
+/* @file JsonPrinter.hpp
+ *
+ * author: Roland Conybeare, Aug 2022
+ */
+
+#pragma once
+
+#include "xo/reflect/Reflect.hpp"
+#include "xo/reflect/TypeDrivenMap.hpp"
+#include "xo/reflect/TaggedPtr.hpp"
+//#include <memory>
+#include <iostream>
+
+namespace xo {
+  namespace json {
+    class PrintJson;
+
+    class JsonPrinter {
+    public:
+      using Reflect = xo::reflect::Reflect;
+      using TaggedPtr = xo::reflect::TaggedPtr;
+      using TypeDescr = xo::reflect::TypeDescr;
+      using TypeId = xo::reflect::TypeId;
+
+    public:
+      JsonPrinter(PrintJson const * pjson) : pjson_{pjson} {}
+      virtual ~JsonPrinter() = default;
+
+      PrintJson const * pjson() const { return pjson_; }
+
+      /* print tagged pointer in json format */
+      virtual void print_json(TaggedPtr tp,
+                  std::ostream * p_os) const = 0;
+
+      void report_internal_type_consistency_error(TypeDescr td1,
+                          TypeDescr td2,
+                          std::ostream * p_os) const;
+
+      /* convenience method for derived printers.
+       * retrieves contents of tp as a T*,  complains to *p_os if that fails.
+       *
+       * (Failure would occur if printer for type T was instead installed
+       *  for some unrelated type U)
+       */
+      template<typename T>
+      T * check_recover_native(TaggedPtr tp, std::ostream * p_os) const {
+    T * x = tp.recover_native<T>();
+
+    if (!x) {
+      this->report_internal_type_consistency_error(Reflect::require<T>(),
+                               tp.td(),
+                               p_os);
+    }
+
+    return x;
+      } /*check_recover_native*/
+
+      void assign_pjson(PrintJson const * pjson) {
+    assert(this->pjson_ == nullptr || this->pjson_ == pjson);
+    this->pjson_ = pjson;
+      } /*assign_pjson*/
+
+    private:
+      /* a json printers is installed into one PrintJson instance;
+       * capture address of that instance at install time
+       */
+      PrintJson const * pjson_ = nullptr;
+    }; /*JsonPrinter*/
+
+    /* AsStringJsonPrinter<T>
+     * prints a T-instance by using operator<< and surrounding in quotes.
+     *
+     * e.g:
+     *   T & x = ..;
+     *   std::ostream * p_os = ..;
+     *
+     *   *p_os << "\"" << x << "\""
+     *
+     */
+    template<typename T>
+    class AsStringJsonPrinter : public JsonPrinter {
+    public:
+      AsStringJsonPrinter(PrintJson const * pjson) : JsonPrinter(pjson) {}
+
+      virtual void print_json(TaggedPtr tp,
+                  std::ostream * p_os) const override
+      {
+    T * x = this->check_recover_native<T>(tp, p_os);
+
+    if(x) {
+      *p_os << "\"" << *x << "\"";
+    }
+      } /*print_json*/
+    }; /*AsStringJsonPrinter*/
+  } /*namespace json*/
+} /*namespace xo*/
+
+
+/* end JsonPrinter.hpp */

include/xo/printjson/PrintJson.hpp

@@ -0,0 +1,143 @@
+/* @file JsonPrinter.hpp
+ *
+ * author: Roland Conybeare, Aug 2022
+ */
+
+#pragma once
+
+#include "JsonPrinter.hpp"
+#include "xo/reflect/TypeDrivenMap.hpp"
+#include "xo/reflect/SelfTagging.hpp"
+#include <memory>
+#include <iostream>
+
+namespace xo {
+    namespace json {
+        class PrintJson : public reflect::SelfTagging {
+        public:
+            using Reflect = xo::reflect::Reflect;
+            using TypeDrivenMap = xo::reflect::TypeDrivenMap<std::unique_ptr<JsonPrinter>>;
+            using SelfTagging = xo::reflect::SelfTagging;
+            using TaggedPtr = xo::reflect::TaggedPtr;
+            using TaggedRcptr = xo::reflect::TaggedRcptr;
+            using TypeDescr = xo::reflect::TypeDescr;
+            using TypeId = xo::reflect::TypeId;
+
+        public:
+            PrintJson();
+            ~PrintJson() = default;
+
+            template<typename T>
+            void print(T const & x_arg, std::ostream * p_os) const {
+                T * x = const_cast<T *>(&x_arg);
+
+                this->print_tp(Reflect::make_tp(x), p_os);
+            } /*print*/
+
+            /* print object tp on stream *p_os, in JSON format;
+             */
+            void print_tp(TaggedPtr tp, std::ostream * p_os) const;
+
+            /* convenience -- shorthand for
+             *   .print(obj->self_tp(), p_os)
+             */
+            void print_obj(ref::rp<SelfTagging> const & obj, std::ostream * p_os) const;
+
+            void provide_printer(TypeId id, std::unique_ptr<JsonPrinter> p) {
+                *(printer_map_.require(id)) = std::move(p);
+            }
+
+            void provide_printer(TypeDescr td, std::unique_ptr<JsonPrinter> p) {
+                this->provide_printer(td->id(), std::move(p));
+            }
+
+            /* write json representation for tp on *p_os */
+            void print_aux(TaggedPtr tp, std::ostream * p_os) const;
+
+            // ----- inherited from SelfTagging -----
+
+            virtual TaggedRcptr self_tp();
+
+        private:
+            /* provide printers for common basic types */
+            void provide_std_printers();
+
+        private:
+            /* map contains specialized printers for specific c++ types */
+            TypeDrivenMap printer_map_;
+        }; /*PrintJson*/
+
+        /* Using singleton here to collect type-specific json printers,
+         * collected during program initialization.
+         *
+         * Could relabel as PrintJsonInitContext if desired
+         */
+        class PrintJsonSingleton {
+        public:
+            static ref::rp<PrintJson> instance();
+
+        private:
+            /* we don't need this to be stored as pointer.
+             * memory burned if unused will be one empty std::vector<>
+             */
+            static ref::rp<PrintJson> s_instance;
+        }; /*PrintJsonSingleton*/
+
+    } /*namespace json*/
+
+#ifdef NOT_USING
+    namespace print {
+        using PrintJson = xo::json::PrintJson;
+
+        /* stream inserter for printing a T-instance in json format */
+        template<typename T>
+        class jsonp_impl {
+        public:
+            jsonp_impl(T const & x, PrintJson const * pjson) : value_(x), pjson_{pjson} {}
+            //jsonp_impl(T const & x, PrintJson const * pjson) : value_{x}, pjson_{pjson} {}
+            //jsonp_impl(T && x, PrintJson const * pjson) : value_(std::move(x)), pjson_{pjson} {}
+
+            void print(std::ostream & os) const {
+                using xo::reflect::Reflect;
+
+                this->pjson_->print_tp(Reflect::make_tp(&value_), &os);
+            } /*print*/
+
+        private:
+            /* value, to be printed, in json format */
+            T value_;
+            /* json printer (bc we don't care for singletons) */
+            PrintJson const * pjson_ = nullptr;
+        }; /*jsonp_impl*/
+
+        template<typename T>
+        inline
+        std::ostream & operator<<(std::ostream & os, jsonp_impl<T> const & x) {
+            x.print(os);
+            return os;
+        } /*operator<<*/
+
+        /* writing out std::forward<T> behavior for completeness' sake:
+         *
+         * 1. call jsonp(x) with rvalue std::string x, then:
+         *    - T will be deduced to [std::string]
+         *        (in particular: _not_ std::string &, std::string const &, std::string &&)
+         *    - rvalue std::string passed to jsonp_impl ctor
+         *
+         * 2a. call jsonp(x) with std::string & x, then:
+         *    - T deduced to [std::string &]
+         *    - std::string & passed to jsonp_impl ctor
+         *
+         * 2b. call jsonp(x) with std::string const & x, then:
+         *    - T deduced to [std::string const &]
+         *    - std::string const & passed to jsonp_impl ctor
+         */
+        template<typename T>
+        auto jsonp(T && x, PrintJson const * pjson) {
+            return jsonp_impl<T>(std::forward<T>(x), pjson);
+        } /*jsonp*/
+    } /*namespace print*/
+#endif
+} /*namespace xo*/
+
+/* end JsonPrinter.hpp */

include/xo/printjson/init_printjson.hpp

@@ -0,0 +1,29 @@
+/* file init_printjson.hpp
+ *
+ * author: Roland Conybeare, Sep 2022
+ */
+
+#pragma once
+
+#include "xo/subsys/Subsystem.hpp"
+
+namespace xo {
+  /* tag to represent the printjson/ subsystem within ordered initialization */
+  enum S_printjson_tag {};
+
+  /* Use:
+   *   // anywhere, to declare printjson dependency  e.g. at file scope
+   *   InitEvidence s_evidence = InitSubsys<S_printjson_tag>::require();
+   *
+   *   // from main(), though can resort to module initialization in a pybind11 library
+   *   Subsystem::initialize_all();
+   */
+  template<>
+  struct InitSubsys<S_printjson_tag> {
+    static void init();
+    static InitEvidence require();
+  };
+} /*namespace xo*/
+
+
+/* end init_printjson.hpp */

src/printjson/CMakeLists.txt

@@ -0,0 +1,13 @@
+# xo-printjson/src/printjson/CMakeLists.txt
+
+set(SELF_LIB printjson)
+set(SELF_SRCS PrintJson.cpp init_printjson.cpp)
+
+xo_add_shared_library(${SELF_LIB} ${PROJECT_VERSION} 1 ${SELF_SRCS})
+
+# ----------------------------------------------------------------
+# dependencies: indentlog, ...
+
+xo_dependency(${SELF_LIB} reflect)
+
+# end CMakeLists.txt

src/printjson/PrintJson.cpp

@@ -0,0 +1,398 @@
+/* file JsonPrinter.cpp
+ *
+ * author: Roland Conybeare, Aug 2022
+ */
+
+#include "PrintJson.hpp"
+//#include "time/Time.hpp"
+#include "xo/reflect/TypeDescr.hpp"
+#include "xo/indentlog/print/tag.hpp"
+#include <cmath>
+
+namespace xo {
+    using xo::time::utc_nanos;
+    using xo::reflect::Metatype;
+    using xo::reflect::Reflect;
+    using xo::reflect::SelfTagging;
+    using xo::reflect::TypeDescr;
+    using xo::reflect::TaggedPtr;
+    using xo::reflect::TaggedRcptr;
+    using xo::time::iso8601;
+    using xo::ref::rp;
+    using xo::xtag;
+
+    namespace json {
+        TaggedRcptr
+        PrintJson::self_tp()
+        {
+            return Reflect::make_rctp(this);
+            //return TaggedRcptr::make(this);
+        } /*self_tp*/
+
+        void
+        JsonPrinter::report_internal_type_consistency_error(TypeDescr td1,
+                                                            TypeDescr td2,
+                                                            std::ostream * p_os) const
+        {
+            *p_os << "<internal-error: type mismatch between T & S"
+                  << xtag("T", td1->canonical_name())
+                  << xtag("S", td2->canonical_name())
+                  << ">";
+        } /*report_internal_type_consistency_error*/
+
+        namespace {
+            /* this will be used when TaggedPtr refers to a pointer-like value,
+             * e.g.
+             *    xo::ref::rp<T>
+             */
+            void
+            print_generic_pointer(PrintJson const & print_json,
+                                  TaggedPtr tp,
+                                  std::ostream * p_os)
+            {
+                /* e.g. if
+                 *   xo::ref::rp<VanillaOption> opt = ...;
+                 * then expect to print just as we would for
+                 *   VanillaOption & opt = ...;
+                 * if pointer is null,  will print {}
+                 */
+
+                if (tp.n_child()) {
+                    print_json.print_aux(tp.get_child(0), p_os);
+                } else {
+                    /* note: this can be distinguished from a bona fide struct,
+                     * b/c it doesn't supply the _name_ member
+                     */
+                    *p_os << "{}";
+                }
+            } /*print_generic_pointer*/
+
+            /* this will be used when TaggedPtr refers to a vector-like value,
+             * e.g.
+             *    std::vector<T>
+             *    std::array<T, N>
+             */
+            void
+            print_generic_vector(PrintJson const & print_json,
+                                 TaggedPtr tp,
+                                 std::ostream * p_os)
+            {
+                /* e.g. if
+                 *   std::array<double, 3> v{1, 2, 3};
+                 *
+                 * then expect to print
+                 *   [1.0, 2.0, 3.0]
+                 */
+
+                *p_os << "[";
+
+                for (uint32_t i = 0, n = tp.n_child(); i < n; ++i) {
+                    if (i > 0)
+                        *p_os << ", ";
+
+                    print_json.print_aux(tp.get_child(i), p_os);
+                }
+
+                *p_os << "]";
+            } /*print_generic_vector*/
+
+            /* this will be used when TaggedPtr is understood to refer to a struct-like value.
+             */
+            void
+            print_generic_struct(PrintJson const & print_json,
+                                 TaggedPtr tp,
+                                 std::ostream * p_os)
+            {
+                /* e.g. if
+                 *   struct Foo { int x_; double y_; };
+                 *   Foo foo{1, 1.4142};
+                 *
+                 * then expect to print
+                 *   {"_name_": "Foo", "x": 1, "y": 1.4142}
+                 *
+                 * note that python json parser requires property names in double quotes
+                 */
+
+                *p_os << "{";
+
+                *p_os << "\"_name_\": \"" << tp.td()->short_name() << "\"";
+
+                for (uint32_t i = 0, n = tp.n_child(); i < n; ++i) {
+                    *p_os << ", \"" << tp.struct_member_name(i) << "\": ";
+
+                    print_json.print_aux(tp.get_child(i), p_os);
+                }
+
+                *p_os << "}";
+            } /*print_generic_struct*/
+
+        } /*namespace*/
+
+        void
+        PrintJson::print_aux(TaggedPtr tp,
+                             std::ostream * p_os) const
+        {
+            if (tp.td()) {
+                TypeId id = tp.td()->id();
+
+                std::unique_ptr<JsonPrinter> const * printer
+                    = this->printer_map_.lookup(id);
+
+                if (printer && *printer) {
+                    (*printer)->print_json(tp, p_os);
+                } else {
+                    /* if no special-case printer,  apply generic printing behavior */
+                    switch (tp.td()->metatype()) {
+                    case Metatype::mt_pointer:
+                        print_generic_pointer(*this, tp, p_os);
+                        return;
+                    case Metatype::mt_vector:
+                        print_generic_vector(*this, tp, p_os);
+                        return;
+                    case Metatype::mt_struct:
+                        print_generic_struct(*this, tp, p_os);
+                        return;
+                    case Metatype::mt_invalid:
+                    case Metatype::mt_atomic:
+                        break;
+                    }
+
+                    (*p_os) << "<error-json-printer-not-found"
+                            << xtag("type", tp.td()->canonical_name())
+                            << xtag("metatype", tp.td()->metatype())
+                            << ">";
+                }
+            } else {
+                (*p_os) << "<error-null-tp>";
+            }
+        } /*print_aux*/
+
+        void
+        PrintJson::print_tp(TaggedPtr tp,
+                            std::ostream * p_os) const
+        {
+            this->print_aux(tp, p_os);
+            //*p_os << std::ends;
+        } /*print*/
+
+        void
+        PrintJson::print_obj(rp<SelfTagging> const & obj, std::ostream * p_os) const
+        {
+            assert(obj.get());
+
+            this->print_tp(obj->self_tp(), p_os);
+        } /*print_obj*/
+
+        class JsonPrinter_bool : public JsonPrinter {
+        public:
+            JsonPrinter_bool(PrintJson const * pjson) : JsonPrinter(pjson) {}
+
+            virtual void print_json(TaggedPtr tp,
+                                    std::ostream * p_os) const override {
+                bool * x = this->check_recover_native<bool>(tp, p_os);
+
+                if (x) {
+                    /* json boolean format is lower case true/false.
+                     * (note that this conflicts with python True/False,  achtung!)
+                     */
+                    *p_os << (*x ? "true" : "false");
+                }
+            } /*print_json*/
+        }; /*JsonPrinter_bool*/
+
+        namespace {
+            void
+            provide_bool_printer(PrintJson * p_json)
+            {
+                std::unique_ptr<JsonPrinter> printer(new JsonPrinter_bool(p_json));
+
+                p_json->provide_printer(Reflect::require<bool>(),
+                                        std::move(printer));
+            } /*provide_bool_printer*/
+        } /*namespace*/
+
+        template<typename T>
+        class JsonPrinter_integer : public JsonPrinter {
+        public:
+            JsonPrinter_integer(PrintJson const * pjson) : JsonPrinter(pjson) {}
+
+            virtual void print_json(TaggedPtr tp,
+                                    std::ostream * p_os) const override {
+                T * x = tp.recover_native<T>();
+
+                if (x) {
+                    *p_os << *x;
+                } else {
+                    report_internal_type_consistency_error(Reflect::require<T>(),
+                                                           tp.td(),
+                                                           p_os);
+                }
+            } /*print_json*/
+        }; /*JsonPrinter_integer*/
+
+        namespace {
+            template<typename T>
+            void
+            provide_integer_printer(PrintJson * p_json)
+            {
+                std::unique_ptr<JsonPrinter> printer(new JsonPrinter_integer<T>(p_json));
+
+                p_json->provide_printer(Reflect::require<T>(), std::move(printer));
+            } /*provide_integer_printer*/
+        }
+
+        template<typename T>
+        class JsonPrinter_floatingpoint : public JsonPrinter {
+        public:
+            JsonPrinter_floatingpoint(PrintJson const * pjson) : JsonPrinter(pjson) {}
+
+            virtual void print_json(TaggedPtr tp,
+                                    std::ostream * p_os) const override
+                {
+                    T * x = tp.recover_native<T>();
+
+                    if (x) {
+                        if (std::isfinite(*x)) {
+                            *p_os << *x;
+                        } else {
+                            /* special cases.
+                             * use javascript-friendly format
+                             *
+                             * Note non-finite floating-point values are not representable in
+                             *      standard json (?!#),  though it's a standard extension
+                             */
+
+                            if (std::isnan(*x))
+                                *p_os << "NaN";
+                            else if (*x > 0.0)
+                                *p_os << "Infinity";
+                            else
+                                *p_os << "-Infinity";
+                        }
+                    } else {
+                        report_internal_type_consistency_error(Reflect::require<T>(),
+                                                               tp.td(),
+                                                               p_os);
+                    }
+                } /*print_json*/
+        }; /*JsonPrinter_floatingpoint*/
+
+        namespace {
+            template<typename T>
+            void
+            provide_floatingpoint_printer(PrintJson * p_json)
+            {
+                std::unique_ptr<JsonPrinter> printer(new JsonPrinter_floatingpoint<T>(p_json));
+
+                p_json->provide_printer(Reflect::require<T>(), std::move(printer));
+            } /*provide_floatingpoint_printer*/
+        } /*namespace*/
+
+        template<typename T>
+        class JsonPrinter_string : public JsonPrinter {
+        public:
+            JsonPrinter_string(PrintJson const * pjson) : JsonPrinter(pjson) {}
+
+            virtual void print_json(TaggedPtr tp,
+                                    std::ostream * p_os) const override {
+                T * x = tp.recover_native<T>();
+
+                if (x) {
+                    /* TODO: escapes special characters */
+                    *p_os << *x;
+                } else {
+                    report_internal_type_consistency_error(Reflect::require<T>(),
+                                                           tp.td(),
+                                                           p_os);
+                }
+            } /*print_json*/
+        }; /*JsonPrinter_string*/
+
+        namespace {
+            template<typename T>
+            void
+            provide_string_printer(PrintJson * p_json)
+            {
+                std::unique_ptr<JsonPrinter> printer(new JsonPrinter_string<T>(p_json));
+
+                p_json->provide_printer(Reflect::require<T>(), std::move(printer));
+            } /*provide_string_printer*/
+        } /*namespace */
+
+        class JsonPrinter_utc_nanos : public JsonPrinter {
+        public:
+            JsonPrinter_utc_nanos(PrintJson * pjson) : JsonPrinter(pjson) {}
+
+            virtual void print_json(TaggedPtr tp,
+                                    std::ostream * p_os) const override {
+                utc_nanos * x = tp.recover_native<utc_nanos>();
+
+                if (x) {
+                    /* format like
+                     *   "2012-04-23T18:25:43.511Z"
+                     * since that's what javascript uses
+                     */
+                    *p_os << "\"" << iso8601(*x) << "\"";
+                } else {
+                    report_internal_type_consistency_error(Reflect::require<utc_nanos>(),
+                                                           tp.td(),
+                                                           p_os);
+                }
+            } /*print_json*/
+        }; /*JsonPrinter_utc_nanos*/
+
+        namespace {
+            void
+            provide_utc_nanos_printer(PrintJson * p_json)
+            {
+                std::unique_ptr<JsonPrinter> printer(new JsonPrinter_utc_nanos(p_json));
+
+                p_json->provide_printer(Reflect::require<utc_nanos>(),
+                                        std::move(printer));
+            } /*provide_utc_nanos_printer*/
+        } /*namespace*/
+
+        PrintJson::PrintJson() {
+            this->provide_std_printers();
+        } /*ctor*/
+
+        /* provide printers for common basic types */
+        void
+        PrintJson::provide_std_printers()
+        {
+            provide_bool_printer(this);
+
+            provide_integer_printer<std::int16_t>(this);
+            provide_integer_printer<std::uint16_t>(this);
+            provide_integer_printer<std::int32_t>(this);
+            provide_integer_printer<std::uint32_t>(this);
+            provide_integer_printer<std::int64_t>(this);
+            provide_integer_printer<std::uint64_t>(this);
+
+            provide_floatingpoint_printer<float>(this);
+            provide_floatingpoint_printer<double>(this);
+
+            provide_string_printer<char *>(this);
+            provide_string_printer<char const *>(this);
+            provide_string_printer<std::string>(this);
+            provide_string_printer<std::string_view>(this);
+
+            provide_utc_nanos_printer(this);
+        } /*provide_std_printers*/
+
+        rp<PrintJson>
+        PrintJsonSingleton::s_instance;
+
+        rp<PrintJson>
+        PrintJsonSingleton::instance()
+        {
+            if (!s_instance)
+                s_instance = new PrintJson();
+
+            return s_instance;
+        } /*instance*/
+
+    } /*namespace json*/
+} /*namespace xo*/
+
+/* end JsonPrinter.cpp */

src/printjson/init_printjson.cpp

@@ -0,0 +1,32 @@
+/* file init_printjson.cpp
+ *
+ * author: Roland Conybeare, Sep 2022
+ */
+
+#include "init_printjson.hpp"
+#include "xo/reflect/init_reflect.hpp"
+#include "xo/subsys/Subsystem.hpp"
+
+namespace xo {
+  void
+  InitSubsys<S_printjson_tag>::init()
+  {
+    /* placeholder -- expecting there to be non-trivial content soon */
+  } /*init*/
+
+  InitEvidence
+  InitSubsys<S_printjson_tag>::require()
+  {
+    InitEvidence retval;
+
+    /* subsystem dependencies for printjson/ */
+    retval ^= InitSubsys<S_reflect_tag>::require();
+
+    /* printjson/'s own initialization code */
+    retval ^= Subsystem::provide<S_printjson_tag>("printjson", &init);
+
+    return retval;
+  } /*require*/
+} /*namespace xo*/
+
+/* end init_printjson.cpp */