Address the second review round of json_view element access

From gregmarr's review of #5622:

- begin()/end(): "a null value or a discarded view iterates as an empty
  range", singular like the primitive case before it.
- The class page's list of function groups has no trailing commas.
- document_data::key_equals() compares a key node with a string, for the
  key comparisons that were spelled out in each lookup.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

docs/mkdocs/docs/api/basic_json_view/begin.md

@@ -6,7 +6,7 @@ iterator begin() const noexcept;
 
 Returns an iterator to the first element of an array, or the first member value of an object, in **document order**
 -- the order the values appear in the source text, not sorted by key. A primitive value iterates as a range of one
-element (itself); `#!json null` and a [discarded](is_discarded.md) view iterate as an empty range.
+element (itself), and a `#!json null` value or a [discarded](is_discarded.md) view iterates as an empty range.
 
 ## Return value
 

docs/mkdocs/docs/api/basic_json_view/end.md

@@ -5,9 +5,8 @@ iterator end() const noexcept;
 ```
 
 Returns an iterator to one past the last element of an array, one past the last member value of an object, in
-**document order** -- see [`begin()`](begin.md). A primitive value iterates as a range of one element (itself);
-`#!json null` and a [discarded](is_discarded.md) view iterate as an empty range, so `#!cpp begin() == end()` for
-them.
+**document order** -- see [`begin()`](begin.md). A primitive value iterates as a range of one element (itself), and a
+`#!json null` value or a [discarded](is_discarded.md) view iterates as an empty range (`#!cpp begin() == end()`).
 
 ## Return value
 

docs/mkdocs/docs/api/basic_json_view/index.md

@@ -22,12 +22,12 @@ Moving the document itself does not invalidate its views: the index is heap-allo
 
 `basic_json_view` provides the read-only part of the `BasicJsonType` interface:
 
-- the type-inspection functions,
-- element access,
-- lookup,
-- iteration, and
+- the type-inspection functions
+- element access
+- lookup
+- iteration
 - conversion: [`get<T>()`](get.md), [`get_string()`](get_string.md), [`number_token()`](number_token.md), and
-  [`materialize()`](materialize.md) to build the `BasicJsonType` value of a subtree on demand.
+  [`materialize()`](materialize.md) to build the `BasicJsonType` value of a subtree on demand
 
 [`operator[]`](operator%5B%5D.md), [`at`](at.md), [`contains`](contains.md), and [`value`](value.md) also accept a
 [`json_pointer`](../json_pointer/index.md). It does not (yet) provide `dump()` or comparison. Unlike `basic_json`,

include/nlohmann/detail/view/document_data.hpp

@@ -10,7 +10,7 @@
 
 #include <array> // array
 #include <cstddef> // size_t
-#include <cstring> // memcpy
+#include <cstring> // memcmp, memcpy
 #include <limits> // numeric_limits
 #include <new> // bad_alloc, operator new, placement new
 #include <string> // string
@@ -141,6 +141,12 @@ struct document_data
         return base[n.flags & node_flags::storage] + n.off;
     }
 
+    /// whether the string of node k (a key) is the n bytes at key
+    bool key_equals(const node& k, const char* key, std::size_t n) const noexcept
+    {
+        return k.len == n && (n == 0 || std::memcmp(str(k), key, n) == 0);
+    }
+
     /// the node after n's subtree (containers span `next` nodes, scalars one)
     static NLOHMANN_VIEW_ALWAYS_INLINE const node* after(const node* n) noexcept
     {

include/nlohmann/detail/view/lookup.hpp

@@ -105,7 +105,7 @@ inline const node* find_member(const document_data& d, const node* object, const
     }
     for (const node* m = document_data::first_child(object); m != end; m = document_data::after(m + 1))
     {
-        if (m->len == n && std::memcmp(d.str(*m), key, n) == 0)
+        if (d.key_equals(*m, key, n))
         {
             return m;
         }
@@ -120,7 +120,7 @@ inline std::size_t count_members(const document_data& d, const node* object, con
     const node* const end = document_data::child_end(object);
     for (const node* m = document_data::first_child(object); m != end; m = document_data::after(m + 1))
     {
-        if (m->len == n && (n == 0 || std::memcmp(d.str(*m), key, n) == 0))
+        if (d.key_equals(*m, key, n))
         {
             ++result;
         }