kind() -- 수신자
- JSON
Value - 최소 인자 수
- 0
- 최대 인자 수
- 0
Declaration and parameters
링크사용 조건
기본 포함 · 미정
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.
수신자
JSONValue
매개변수 제약
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.
결과
The declared result type is string.
효과
실패
Result and effects
링크The 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
링크One query covers every JSON kind, and ordinary equality expresses each kind test.
Related entries
링크Inspect JSON kinds with kind
링크Inspect 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.
이유
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
링크import 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
기대 결과
기대 결과
실행을 마칩니다. 종료 코드 0.
null:truebool:falsenumber:falsestring:falsearray:falseobject:false
Keep present null values distinct from missing entries
링크import 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
기대 결과
기대 결과
실행을 마칩니다. 종료 코드 0.
null:null
Reject the removed JSONValue.isNull member
링크import std.json { JSONValue }function inspect(value: JSONValue) -> () {let result = value.isNull()return ()}
표준 출력 없음.기대 결과
Use kind to test a JSON value for null
링크import std.json { JSONValue }function inspect(value: JSONValue) -> () {let result = value.kind() == "null"return ()}
표준 출력 없음.기대 결과
기대 결과
검사가 프로그램을 받아들입니다. 종료 코드 0.