Document and test first-wins lookups next to dump() and ==

dump() writes every member and == resolves duplicate keys as parse()
does, whereas lookups find the first member of a duplicate key.

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

docs/mkdocs/docs/api/basic_json_view/operator_eq.md

@@ -18,6 +18,8 @@ bool operator==(const BasicJsonType& lhs, const basic_json_view& rhs);
 Neither overload builds a `BasicJsonType` value for a view to do the comparison (see [Notes](#notes) below). Numbers
 compare by value across their types (`#!cpp 1 == 1.0`), and an object compares by its members, with duplicate keys
 resolved exactly as `parse()` resolves them -- the last value, at the position of the first occurrence of the key.
+This is not what [`operator[]`](operator[].md) and the other lookups return for a duplicate key: they find the *first*
+member (see [Duplicate keys](../../features/json_view.md#duplicate-keys)).
 
 ## Parameters
 

docs/mkdocs/docs/features/json_view.md

@@ -221,8 +221,8 @@ Both results are only valid as long as the view -- and, for a string with no esc
 [`dump()`](../api/basic_json_view/dump.md) serializes a view directly from the flat index, without ever building a
 `basic_json` value. An object's members are written in document order, not sorted by key, and *every* occurrence of a
 repeated key is written, not only the last one -- the same two ways [iteration](#what-is-different) already differs
-from a [`materialize()`](../api/basic_json_view/materialize.md)d value, see above. `#!cpp materialize().dump()` gives
-a different result in both respects for a `json_view`.
+from a [`materialize()`](../api/basic_json_view/materialize.md)d value, see [Duplicate keys](#duplicate-keys).
+`#!cpp materialize().dump()` gives a different result in both respects for a `json_view`.
 
 By default, numbers are written the way [`basic_json::dump()`](../api/basic_json/dump.md) would.
 [`number_format::source`](../api/basic_json_view/number_format.md) instead copies every number exactly as it was

tests/src/unit-json_view.cpp

@@ -1461,6 +1461,8 @@ TEST_CASE("json_view dump")
         const json_document d = json_document::parse(R"({"b": 1, "a": 2, "b": 3})");
         CHECK(d.root().dump() == R"({"b":1,"a":2,"b":3})");
         CHECK(d.root().dump(1) == "{\n \"b\": 1,\n \"a\": 2,\n \"b\": 3\n}");
+        // dump() writes all members, though the lookup finds the first
+        CHECK(d.root()["b"].dump() == "1");
     }
 
     SECTION("deep nesting")
@@ -1583,6 +1585,9 @@ TEST_CASE("json_view comparison")
         const ordered_json_document dup = ordered_json_document::parse(R"({"a": 1, "b": 2, "a": 3})");
         const ordered_json_document last = ordered_json_document::parse(R"({"a": 3, "b": 2})");
         CHECK(dup.root() == last.root());
+        // (== compares as parse() resolves duplicates, a lookup finds the first)
+        CHECK(dup.root()["a"].materialize() == 1);
+        CHECK(dup.root()["a"] != last.root()["a"]);
         const ordered_json_document ab = ordered_json_document::parse(R"({"a": 1, "b": 2})");
         const ordered_json_document ba = ordered_json_document::parse(R"({"b": 2, "a": 1})");
         CHECK(ab.root() != ba.root());