Add support for C++ 20 ranges. (#1050)

C++ 20 adds a new feature called "ranges", which provides components for dealing
with sequences of values: https://en.cppreference.com/w/cpp/ranges.

A range is like a normal object containing `begin` and `end`, except there are
also composable operations like maps, filters, joins, etc.
The iterator objects returned by a range's `begin` and `end` require a more
strict set of operations than is needed for a range-for loop.

This PR adds the extra operations needed to support turning `dom::array` and
`dom::object` into a range.
This PR does not depend on any C++ 20 behavior, the added operators are all
valid C++ 11, and are already part of the LegacyIterator concepts.
This PR adds extra code behind: `#if defined(__cpp_lib_ranges)` guards, which is
the new C++ 20 specified feature test macro for ranges support. When ranges
support is detected, extra compile time checks are added to ensure that
`dom::array` and `dom::object` satisfy the range concept. No runtime tests have
been added yet because these compile time checks should be sufficient.

If desired, the `static_assert` code could be moved out of the actual code
headers and put into a test file.

include/simdjson/dom/array.h

@@ -23,10 +23,13 @@ public:
 
   class iterator {
   public:
+    using value_type = element;
+    using difference_type = std::ptrdiff_t;
+
     /**
      * Get the actual value
      */
-    inline element operator*() const noexcept;
+    inline value_type operator*() const noexcept;
     /**
      * Get the next value.
      *
@@ -34,12 +37,28 @@ public:
      *
      */
     inline iterator& operator++() noexcept;
+    /**
+     * Get the next value.
+     *
+     * Part of the  std::iterator interface.
+     */
+    inline iterator operator++(int) noexcept;
     /**
      * Check if these values come from the same place in the JSON.
      *
      * Part of the std::iterator interface.
      */
     inline bool operator!=(const iterator& other) const noexcept;
+    inline bool operator==(const iterator& other) const noexcept;
+
+    inline bool operator<(const iterator& other) const noexcept;
+    inline bool operator<=(const iterator& other) const noexcept;
+    inline bool operator>=(const iterator& other) const noexcept;
+    inline bool operator>(const iterator& other) const noexcept;
+
+    iterator() noexcept = default;
+    iterator(const iterator&) noexcept = default;
+    iterator& operator=(const iterator&) noexcept = default;
   private:
     really_inline iterator(const internal::tape_ref &tape) noexcept;
     internal::tape_ref tape;
@@ -155,4 +174,16 @@ inline std::ostream& operator<<(std::ostream& out, const simdjson_result<dom::ar
 
 } // namespace simdjson
 
+#if defined(__cpp_lib_ranges)
+#include <ranges>
+
+namespace std::ranges {
+template<>
+inline constexpr bool enable_view<simdjson::dom::array> = true;
+}
+
+static_assert(std::ranges::view<simdjson::dom::array>);
+static_assert(std::ranges::sized_range<simdjson::dom::array>);
+#endif
+
 #endif // SIMDJSON_DOM_ARRAY_H

include/simdjson/dom/object.h

@@ -24,10 +24,13 @@ public:
 
   class iterator {
   public:
+    using value_type = key_value_pair;
+    using difference_type = std::ptrdiff_t;
+
     /**
      * Get the actual key/value pair
      */
-    inline const key_value_pair operator*() const noexcept;
+    inline const value_type operator*() const noexcept;
     /**
      * Get the next key/value pair.
      *
@@ -36,11 +39,24 @@ public:
      */
     inline iterator& operator++() noexcept;
     /**
-     * Check if these key value pairs come from the same place in the JSON.
+     * Get the next key/value pair.
+     *
+     * Part of the std::iterator interface.
+     *
+     */
+    inline iterator operator++(int) noexcept;
+    /**
+     * Check if these values come from the same place in the JSON.
      *
      * Part of the std::iterator interface.
      */
     inline bool operator!=(const iterator& other) const noexcept;
+    inline bool operator==(const iterator& other) const noexcept;
+
+    inline bool operator<(const iterator& other) const noexcept;
+    inline bool operator<=(const iterator& other) const noexcept;
+    inline bool operator>=(const iterator& other) const noexcept;
+    inline bool operator>(const iterator& other) const noexcept;
     /**
      * Get the key of this key/value pair.
      */
@@ -69,6 +85,10 @@ public:
      * Get the value of this key/value pair.
      */
     inline element value() const noexcept;
+
+    iterator() noexcept = default;
+    iterator(const iterator&) noexcept = default;
+    iterator& operator=(const iterator&) noexcept = default;
   private:
     really_inline iterator(const internal::tape_ref &tape) noexcept;
 
@@ -261,4 +281,16 @@ inline std::ostream& operator<<(std::ostream& out, const simdjson_result<dom::ob
 
 } // namespace simdjson
 
+#if defined(__cpp_lib_ranges)
+#include <ranges>
+
+namespace std::ranges {
+template<>
+inline constexpr bool enable_view<simdjson::dom::object> = true;
+}
+
+static_assert(std::ranges::view<simdjson::dom::object>);
+static_assert(std::ranges::sized_range<simdjson::dom::object>);
+#endif
+
 #endif // SIMDJSON_DOM_OBJECT_H

include/simdjson/inline/array.h

@@ -106,14 +106,33 @@ really_inline array::iterator::iterator(const internal::tape_ref &_tape) noexcep
 inline element array::iterator::operator*() const noexcept {
   return element(tape);
 }
-inline bool array::iterator::operator!=(const array::iterator& other) const noexcept {
-  return tape.json_index != other.tape.json_index;
-}
 inline array::iterator& array::iterator::operator++() noexcept {
   tape.json_index = tape.after_element();
   return *this;
 }
-
+inline array::iterator array::iterator::operator++(int) noexcept {
+  array::iterator out = *this;
+  ++*this;
+  return out;
+}
+inline bool array::iterator::operator!=(const array::iterator& other) const noexcept {
+  return tape.json_index != other.tape.json_index;
+}
+inline bool array::iterator::operator==(const array::iterator& other) const noexcept {
+  return tape.json_index == other.tape.json_index;
+}
+inline bool array::iterator::operator<(const array::iterator& other) const noexcept {
+  return tape.json_index < other.tape.json_index;
+}
+inline bool array::iterator::operator<=(const array::iterator& other) const noexcept {
+  return tape.json_index <= other.tape.json_index;
+}
+inline bool array::iterator::operator>=(const array::iterator& other) const noexcept {
+  return tape.json_index >= other.tape.json_index;
+}
+inline bool array::iterator::operator>(const array::iterator& other) const noexcept {
+  return tape.json_index > other.tape.json_index;
+}
 inline std::ostream& operator<<(std::ostream& out, const array &value) {
   return out << minify<array>(value);
 }

include/simdjson/inline/object.h

@@ -149,11 +149,31 @@ inline const key_value_pair object::iterator::operator*() const noexcept {
 inline bool object::iterator::operator!=(const object::iterator& other) const noexcept {
   return tape.json_index != other.tape.json_index;
 }
+inline bool object::iterator::operator==(const object::iterator& other) const noexcept {
+  return tape.json_index == other.tape.json_index;
+}
+inline bool object::iterator::operator<(const object::iterator& other) const noexcept {
+  return tape.json_index < other.tape.json_index;
+}
+inline bool object::iterator::operator<=(const object::iterator& other) const noexcept {
+  return tape.json_index <= other.tape.json_index;
+}
+inline bool object::iterator::operator>=(const object::iterator& other) const noexcept {
+  return tape.json_index >= other.tape.json_index;
+}
+inline bool object::iterator::operator>(const object::iterator& other) const noexcept {
+  return tape.json_index > other.tape.json_index;
+}
 inline object::iterator& object::iterator::operator++() noexcept {
   tape.json_index++;
   tape.json_index = tape.after_element();
   return *this;
 }
+inline object::iterator object::iterator::operator++(int) noexcept {
+  object::iterator out = *this;
+  ++*this;
+  return out;
+}
 inline std::string_view object::iterator::key() const noexcept {
   return tape.get_string_view();
 }

singleheader/amalgamate_demo.cpp

@@ -1,4 +1,4 @@
-/* auto-generated on Mon Jul  6 18:16:52 EDT 2020. Do not edit! */
+/* auto-generated on Sun 19 Jul 2020 11:55:45 PM EDT. Do not edit! */
 
 #include <iostream>
 #include "simdjson.h"

singleheader/simdjson.cpp

@@ -1,4 +1,4 @@
-/* auto-generated on Mon Jul  6 18:16:52 EDT 2020. Do not edit! */
+/* auto-generated on Sun 19 Jul 2020 11:55:45 PM EDT. Do not edit! */
 /* begin file src/simdjson.cpp */
 #include "simdjson.h"
 
@@ -4610,7 +4610,7 @@ namespace logger {
 namespace stage2 {
 namespace atomparsing {
 
-really_inline uint32_t string_to_uint32(const char* str) { return *reinterpret_cast<const uint32_t *>(str); }
+really_inline uint32_t string_to_uint32(const char* str) { uint32_t val; std::memcpy(&val, str, sizeof(uint32_t)); return val; }
 
 WARN_UNUSED
 really_inline uint32_t str4ncmp(const uint8_t *src, const char* atom) {
@@ -6704,7 +6704,7 @@ namespace logger {
 namespace stage2 {
 namespace atomparsing {
 
-really_inline uint32_t string_to_uint32(const char* str) { return *reinterpret_cast<const uint32_t *>(str); }
+really_inline uint32_t string_to_uint32(const char* str) { uint32_t val; std::memcpy(&val, str, sizeof(uint32_t)); return val; }
 
 WARN_UNUSED
 really_inline uint32_t str4ncmp(const uint8_t *src, const char* atom) {
@@ -9926,7 +9926,7 @@ namespace logger {
 namespace stage2 {
 namespace atomparsing {
 
-really_inline uint32_t string_to_uint32(const char* str) { return *reinterpret_cast<const uint32_t *>(str); }
+really_inline uint32_t string_to_uint32(const char* str) { uint32_t val; std::memcpy(&val, str, sizeof(uint32_t)); return val; }
 
 WARN_UNUSED
 really_inline uint32_t str4ncmp(const uint8_t *src, const char* atom) {
@@ -13124,7 +13124,7 @@ namespace logger {
 namespace stage2 {
 namespace atomparsing {
 
-really_inline uint32_t string_to_uint32(const char* str) { return *reinterpret_cast<const uint32_t *>(str); }
+really_inline uint32_t string_to_uint32(const char* str) { uint32_t val; std::memcpy(&val, str, sizeof(uint32_t)); return val; }
 
 WARN_UNUSED
 really_inline uint32_t str4ncmp(const uint8_t *src, const char* atom) {

singleheader/simdjson.h

@@ -1,4 +1,4 @@
-/* auto-generated on Mon Jul  6 18:16:52 EDT 2020. Do not edit! */
+/* auto-generated on Sun 19 Jul 2020 11:55:45 PM EDT. Do not edit! */
 /* begin file include/simdjson.h */
 #ifndef SIMDJSON_H
 #define SIMDJSON_H
@@ -3073,10 +3073,13 @@ public:
 
   class iterator {
   public:
+    using value_type = element;
+    using difference_type = std::ptrdiff_t;
+
     /**
      * Get the actual value
      */
-    inline element operator*() const noexcept;
+    inline value_type operator*() const noexcept;
     /**
      * Get the next value.
      *
@@ -3084,12 +3087,28 @@ public:
      *
      */
     inline iterator& operator++() noexcept;
+    /**
+     * Get the next value.
+     *
+     * Part of the  std::iterator interface.
+     */
+    inline iterator operator++(int) noexcept;
     /**
      * Check if these values come from the same place in the JSON.
      *
      * Part of the std::iterator interface.
      */
     inline bool operator!=(const iterator& other) const noexcept;
+    inline bool operator==(const iterator& other) const noexcept;
+
+    inline bool operator<(const iterator& other) const noexcept;
+    inline bool operator<=(const iterator& other) const noexcept;
+    inline bool operator>=(const iterator& other) const noexcept;
+    inline bool operator>(const iterator& other) const noexcept;
+
+    iterator() noexcept = default;
+    iterator(const iterator&) noexcept = default;
+    iterator& operator=(const iterator&) noexcept = default;
   private:
     really_inline iterator(const internal::tape_ref &tape) noexcept;
     internal::tape_ref tape;
@@ -3205,6 +3224,18 @@ inline std::ostream& operator<<(std::ostream& out, const simdjson_result<dom::ar
 
 } // namespace simdjson
 
+#if defined(__cpp_lib_ranges)
+#include <ranges>
+
+namespace std::ranges {
+template<>
+inline constexpr bool enable_view<simdjson::dom::array> = true;
+}
+
+static_assert(std::ranges::view<simdjson::dom::array>);
+static_assert(std::ranges::sized_range<simdjson::dom::array>);
+#endif
+
 #endif // SIMDJSON_DOM_ARRAY_H
 /* end file include/simdjson/minify.h */
 /* begin file include/simdjson/dom/document_stream.h */
@@ -4539,10 +4570,13 @@ public:
 
   class iterator {
   public:
+    using value_type = key_value_pair;
+    using difference_type = std::ptrdiff_t;
+
     /**
      * Get the actual key/value pair
      */
-    inline const key_value_pair operator*() const noexcept;
+    inline const value_type operator*() const noexcept;
     /**
      * Get the next key/value pair.
      *
@@ -4551,11 +4585,24 @@ public:
      */
     inline iterator& operator++() noexcept;
     /**
-     * Check if these key value pairs come from the same place in the JSON.
+     * Get the next key/value pair.
+     *
+     * Part of the std::iterator interface.
+     *
+     */
+    inline iterator operator++(int) noexcept;
+    /**
+     * Check if these values come from the same place in the JSON.
      *
      * Part of the std::iterator interface.
      */
     inline bool operator!=(const iterator& other) const noexcept;
+    inline bool operator==(const iterator& other) const noexcept;
+
+    inline bool operator<(const iterator& other) const noexcept;
+    inline bool operator<=(const iterator& other) const noexcept;
+    inline bool operator>=(const iterator& other) const noexcept;
+    inline bool operator>(const iterator& other) const noexcept;
     /**
      * Get the key of this key/value pair.
      */
@@ -4584,6 +4631,10 @@ public:
      * Get the value of this key/value pair.
      */
     inline element value() const noexcept;
+
+    iterator() noexcept = default;
+    iterator(const iterator&) noexcept = default;
+    iterator& operator=(const iterator&) noexcept = default;
   private:
     really_inline iterator(const internal::tape_ref &tape) noexcept;
 
@@ -4776,6 +4827,18 @@ inline std::ostream& operator<<(std::ostream& out, const simdjson_result<dom::ob
 
 } // namespace simdjson
 
+#if defined(__cpp_lib_ranges)
+#include <ranges>
+
+namespace std::ranges {
+template<>
+inline constexpr bool enable_view<simdjson::dom::object> = true;
+}
+
+static_assert(std::ranges::view<simdjson::dom::object>);
+static_assert(std::ranges::sized_range<simdjson::dom::object>);
+#endif
+
 #endif // SIMDJSON_DOM_OBJECT_H
 /* end file include/simdjson/dom/object.h */
 
@@ -5379,14 +5442,33 @@ really_inline array::iterator::iterator(const internal::tape_ref &_tape) noexcep
 inline element array::iterator::operator*() const noexcept {
   return element(tape);
 }
-inline bool array::iterator::operator!=(const array::iterator& other) const noexcept {
-  return tape.json_index != other.tape.json_index;
-}
 inline array::iterator& array::iterator::operator++() noexcept {
   tape.json_index = tape.after_element();
   return *this;
 }
-
+inline array::iterator array::iterator::operator++(int) noexcept {
+  array::iterator out = *this;
+  ++*this;
+  return out;
+}
+inline bool array::iterator::operator!=(const array::iterator& other) const noexcept {
+  return tape.json_index != other.tape.json_index;
+}
+inline bool array::iterator::operator==(const array::iterator& other) const noexcept {
+  return tape.json_index == other.tape.json_index;
+}
+inline bool array::iterator::operator<(const array::iterator& other) const noexcept {
+  return tape.json_index < other.tape.json_index;
+}
+inline bool array::iterator::operator<=(const array::iterator& other) const noexcept {
+  return tape.json_index <= other.tape.json_index;
+}
+inline bool array::iterator::operator>=(const array::iterator& other) const noexcept {
+  return tape.json_index >= other.tape.json_index;
+}
+inline bool array::iterator::operator>(const array::iterator& other) const noexcept {
+  return tape.json_index > other.tape.json_index;
+}
 inline std::ostream& operator<<(std::ostream& out, const array &value) {
   return out << minify<array>(value);
 }
@@ -6659,11 +6741,31 @@ inline const key_value_pair object::iterator::operator*() const noexcept {
 inline bool object::iterator::operator!=(const object::iterator& other) const noexcept {
   return tape.json_index != other.tape.json_index;
 }
+inline bool object::iterator::operator==(const object::iterator& other) const noexcept {
+  return tape.json_index == other.tape.json_index;
+}
+inline bool object::iterator::operator<(const object::iterator& other) const noexcept {
+  return tape.json_index < other.tape.json_index;
+}
+inline bool object::iterator::operator<=(const object::iterator& other) const noexcept {
+  return tape.json_index <= other.tape.json_index;
+}
+inline bool object::iterator::operator>=(const object::iterator& other) const noexcept {
+  return tape.json_index >= other.tape.json_index;
+}
+inline bool object::iterator::operator>(const object::iterator& other) const noexcept {
+  return tape.json_index > other.tape.json_index;
+}
 inline object::iterator& object::iterator::operator++() noexcept {
   tape.json_index++;
   tape.json_index = tape.after_element();
   return *this;
 }
+inline object::iterator object::iterator::operator++(int) noexcept {
+  object::iterator out = *this;
+  ++*this;
+  return out;
+}
 inline std::string_view object::iterator::key() const noexcept {
   return tape.get_string_view();
 }