kind() -- Модуль
- std.
json → - Получатель
- JSON
Value - Минимальное число аргументов
- 0
- Максимальное число аргументов
- 0
Declaration and parameters
СсылкаДоступность
Включено по умолчанию · Не определено
Import std.json in language mode 5.21.
The current compiler selects std/json.tpz for this language mode. Availability in other released editions and inclusion in each installed distribution are Pending.
Получатель
JSONValue
Ограничения параметров
JSON returns exactly one of null, bool, number, string, array, or object. The name describes the JSON value's outermost kind. Both true and false have kind bool. Integer and fractional JSON numbers have kind number.
Test whether a JSON value is null with value.. This comparison is false for false, zero, the empty string, and empty arrays and objects. Reading the kind does not modify or decode the JSON value.
A present array element or object member containing JSON null is still present. at and get return Some(value) containing that JSONValue. An absent element or member returns None(). Inspect presence first, then compare the contained value's kind.
JSONValue does not expose an is member. Use the same kind comparison for null as for every other JSON kind.
Результат
The declared result type is string.
Эффекты
Ошибки
Result and effects
СсылкаThe result is null, bool, number, string, array, or object. Compare it with "null" to test for JSON null. This query preserves the value and distinguishes stored null from an absent array element or object member.
Why
СсылкаOne query covers every JSON kind, and ordinary equality expresses each kind test.
Related entries
СсылкаInspect JSON kinds with kind
СсылкаInspect JSON kinds with kind
JSON returns exactly one of null, bool, number, string, array, or object. The name describes the JSON value's outermost kind. Both true and false have kind bool. Integer and fractional JSON numbers have kind number.
Test whether a JSON value is null with value.. This comparison is false for false, zero, the empty string, and empty arrays and objects. Reading the kind does not modify or decode the JSON value.
A present array element or object member containing JSON null is still present. at and get return Some(value) containing that JSONValue. An absent element or member returns None(). Inspect presence first, then compare the contained value's kind.
JSONValue does not expose an is member. Use the same kind comparison for null as for every other JSON kind.
Причина
One kind query distinguishes every JSON value kind. Comparing that result uses the ordinary equality rule for null, booleans, numbers, strings, arrays, and objects. A separate null predicate would duplicate one case and give it a second spelling. Keeping presence separate also prevents a stored null from being mistaken for a missing entry.
Distinguish null from every other JSON kind
Ссылкаimport std.jsonimport std.testimport std.iofor source in (["null", "false", "0", "\"\"", "[]", "\{\}"]) {let value = test.assertOk(json.parse(source))let kind = value.kind()let nullKind = kind == "null"io.writeLine("{kind}:{nullKind}")}
null:true
bool:false
number:false
string:false
array:false
object:false
Ожидаемый результат
Ожидаемый результат
Выполнение завершается. Код завершения 0.
null:truebool:falsenumber:falsestring:falsearray:falseobject:false
Keep present null values distinct from missing entries
Ссылкаimport std.jsonimport std.testimport std.iolet array = test.assertOk(json.parse("[null]"))let object = test.assertOk(json.parse("\{\"present\":null\}"))let arrayValue = test.assertSome(array.at(0))let objectValue = test.assertSome(object.get("present"))test.assertNone(array.at(1))test.assertNone(object.get("absent"))io.writeLine("{arrayValue.kind()}:{objectValue.kind()}")
null:null
Ожидаемый результат
Ожидаемый результат
Выполнение завершается. Код завершения 0.
null:null
Reject the removed JSONValue.isNull member
Ссылкаimport std.json { JSONValue }function inspect(value: JSONValue) -> () {let result = value.isNull()return ()}
Нет стандартного вывода.Ожидаемый результат
Ожидаемый результат
Этап отклонения check. Ненулевой код завершения.
stdlib-removed-member at
main.tpz:4:22
Use kind to test a JSON value for null
Ссылкаimport std.json { JSONValue }function inspect(value: JSONValue) -> () {let result = value.kind() == "null"return ()}
Нет стандартного вывода.Ожидаемый результат
Ожидаемый результат
Проверка принимает программу. Код завершения 0.