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라이브러리 · std.json

JSONValue.at

Looks up a JSON value by array index.

at(index: int) -> Option<JSONValue>

모듈: std.json →
수신자: JSONValue
최소 인자 수: 1
최대 인자 수: 1

Declaration and parameters

사용 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

추가 계약은 미정입니다.

JSONValue is an immutable JSON tree with the six JSON kinds. Reading a member preserves the tree.

asBool and asString return Some for the matching kind and None() for every other kind. False and empty text are present values. Neither function parses text or converts a number.

numberText returns the exact accepted number lexeme for a number and None() for another kind. It preserves a negative zero, exponent spelling and fractional trailing zeroes.

asInt returns Some for a number spelled as an optional minus and decimal integer digits within the signed 64 bit range. Negative zero becomes zero. A decimal point, exponent, overflow or different kind returns None() without rounding.

asArray returns the elements of an array in source order. Another kind returns None(). The returned array is a separate collection. Changing that collection does not change the JSON tree.

at uses a zero based array index. A negative index, an index at or beyond the array length, or a receiver of another kind returns None(). get uses an exact decoded object key and returns None() for an absent key or another receiver kind. A present null child is Some containing JSON null.

length is a property containing the array element count or object member count. Scalar kinds yield None(). keys and values are object properties. They contain arrays in ascending Unicode scalar order of decoded keys, with corresponding positions. Array and scalar receivers yield None() for both properties.

The receiver and supplied arguments are evaluated once in ordinary call order. Inspection performs no I/O and invokes no user conversion. Incorrect argument types follow ordinary checking diagnostics rather than becoming absent values.

관련 규칙 · Project JSON values without coercion →

결과

추가 계약은 미정입니다.

The declared result type is Option<JSONValue>.

효과

미정

실패

미정

Result and effects

Return the optional array child at a zero based index.

Project JSON values without coercion

규칙topaz.stdlib.contract.json-value.rule

Project JSON values without coercion

JSONValue is an immutable JSON tree with the six JSON kinds. Reading a member preserves the tree.

asBool and asString return Some for the matching kind and None() for every other kind. False and empty text are present values. Neither function parses text or converts a number.

numberText returns the exact accepted number lexeme for a number and None() for another kind. It preserves a negative zero, exponent spelling and fractional trailing zeroes.

asInt returns Some for a number spelled as an optional minus and decimal integer digits within the signed 64 bit range. Negative zero becomes zero. A decimal point, exponent, overflow or different kind returns None() without rounding.

asArray returns the elements of an array in source order. Another kind returns None(). The returned array is a separate collection. Changing that collection does not change the JSON tree.

at uses a zero based array index. A negative index, an index at or beyond the array length, or a receiver of another kind returns None(). get uses an exact decoded object key and returns None() for an absent key or another receiver kind. A present null child is Some containing JSON null.

length is a property containing the array element count or object member count. Scalar kinds yield None(). keys and values are object properties. They contain arrays in ascending Unicode scalar order of decoded keys, with corresponding positions. Array and scalar receivers yield None() for both properties.

The receiver and supplied arguments are evaluated once in ordinary call order. Inspection performs no I/O and invokes no user conversion. Incorrect argument types follow ordinary checking diagnostics rather than becoming absent values.

이유

Optional projection keeps a missing child distinct from a stored null. Number text preserves the original representation, while the integer projection has an explicit spelling and range. Sorted key and value positions support deterministic traversal.

예제 Inspect present values and missing children →Keep integer projection within the declared spelling and range →Read matching keys and values in scalar order →

Inspect present values and missing children

run · running · 검증 · 미실행

main.tpzInspect present values and missing children플레이그라운드 열기 →

import std.json
import std.test
import std.io
let value = test.assertOk(json.parse("[false,\"\",null,7]"))
let items = test.assertSome(value.asArray())
test.assertEq(test.assertSome(items[0].asBool()), false)
test.assertEq(test.assertSome(items[1].asString()), "")
test.assertEq(items[2].kind(), "null")
test.assertEq(test.assertSome(items[3].asInt()), 7)
test.assertNone(value.at(-1))
test.assertNone(value.at(4))
test.assertNone(value.get("0"))
test.assertNone(items[0].asString())
test.assertNone(items[1].numberText())
test.assertNone(items[2].asArray())
let object = test.assertOk(json.parse("\{\"present\":null\}"))
test.assertEq(test.assertSome(object.get("present")).kind(), "null")
test.assertNone(object.get("missing"))
test.assertNone(object.at(0))
io.writeLine("present values remain distinct from missing children")

기대 출력종료 코드 0

present values remain distinct from missing children

$ topaz run main.tpz · 대상 제품 5.21.3

기대 결과

기대 결과

실행을 마칩니다. 종료 코드 0.

표준 오류 출력 없음.

기대 표준 출력

present values remain distinct from missing children

이 예제는 아직 실행하지 않았습니다.

Keep integer projection within the declared spelling and range

run · running · 검증 · 미실행

main.tpzKeep integer projection within the declared spelling and range플레이그라운드 열기 →

import std.json
import std.test
import std.io
for text in (["-9223372036854775808", "9223372036854775807", "9223372036854775808", "-0", "1.0", "1e0", "1.5"]) {
let value = test.assertOk(json.parse(text))
match (value.asInt()) {
case Some(number) => io.writeLine("{text} = {number}")
case None() => io.writeLine("{text} = none")
}
}

기대 출력종료 코드 0

-9223372036854775808 = -9223372036854775808
9223372036854775807 = 9223372036854775807
9223372036854775808 = none
-0 = 0
1.0 = none
1e0 = none
1.5 = none

$ topaz run main.tpz · 대상 제품 5.21.3

기대 결과

기대 결과

실행을 마칩니다. 종료 코드 0.

표준 오류 출력 없음.

기대 표준 출력

-9223372036854775808 = -9223372036854775808
9223372036854775807 = 9223372036854775807
9223372036854775808 = none
-0 = 0
1.0 = none
1e0 = none
1.5 = none

이 예제는 아직 실행하지 않았습니다.

Read matching keys and values in scalar order

run · running · 검증 · 미실행

main.tpzRead matching keys and values in scalar order플레이그라운드 열기 →

import std.json
import std.test
import std.io
let object = test.assertOk(json.parse("\{\"z\":1,\"a\":null\}"))
let names = test.assertSome(object.keys)
let values = test.assertSome(object.values)
test.assertEq(test.assertSome(object.length), 2)
io.writeLine("{names[0]} = {values[0].kind()}")
io.writeLine("{names[1]} = {test.assertSome(values[1].asInt())}")
let array = test.assertOk(json.parse("[]"))
test.assertEq(test.assertSome(array.length), 0)
test.assertNone(array.keys)
test.assertNone(array.values)
let scalar = test.assertOk(json.parse("\"text\""))
test.assertNone(scalar.length)

기대 출력종료 코드 0

a = null
z = 1

$ topaz run main.tpz · 대상 제품 5.21.3

기대 결과

기대 결과

실행을 마칩니다. 종료 코드 0.

표준 오류 출력 없음.

기대 표준 출력

a = null
z = 1

이 예제는 아직 실행하지 않았습니다.