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Test discarded views with is_discarded() in the operator[] docs and examples

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The explicit conversion to bool of basic_json_view is gone.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-10-09 16:54:05 +02:00
parent f60b822476
commit a1d74c55a7
3 changed files with 8 additions and 5 deletions
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8
docs/mkdocs/docs/examples/basic_json_view__operator[].cpp
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@@ -22,17 +22,19 @@ int main()
std::cout << user["name"].materialize().dump();
// operator[] on a missing object key gives a discarded view -- test
// it with a plain "if". The const overload of json::operator[]
// it with is_discarded(). The const overload of json::operator[]
// would instead be undefined behavior (guarded by an assertion) for
// a missing key
if (const auto email = user["email"])
const auto email = user["email"];
if (!email.is_discarded())
{
std::cout << " <" << email.materialize().dump() << ">";
}
// the same holds for an array index past the end: a discarded view,
// not undefined behavior
if (const auto first_tag = user["tags"][0])
const auto first_tag = user["tags"][0];
if (!first_tag.is_discarded())
{
std::cout << " #" << first_tag.materialize().dump();
}

3
docs/mkdocs/docs/examples/basic_json_view__operator[]_json_pointer.cpp
View File

@@ -25,7 +25,8 @@ int main()
// a missing key or an out-of-range index along the path gives a
// discarded view, exactly where const json::operator[] would be
// undefined behavior for the same pointer
if (const auto missing = root[json_pointer("/region/servers/5/metrics/cpu")])
const auto missing = root[json_pointer("/region/servers/5/metrics/cpu")];
if (!missing.is_discarded())
{
std::cout << missing.materialize().dump() << '\n';
}