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Спецификация 6.0

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    Библиотека

    std.json.parseAs

    Parses JSON text into a requested type.

    parseAs<T>(text: string) -> Result<T, string>
    Модуль
    std.json →
    Получатель
    Неприменимо
    Минимальное число аргументов
    1
    Максимальное число аргументов
    1

    Declaration and parameters

    Ссылка

    Доступность

    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

    Неприменимо

    Ограничения параметров

    Дополнительные контракты не определены.

    parseAs<T> requires an explicit JSON decodable result type. The ordinary JSON capability checks apply. Omitting a required result type or selecting a type without decoding support produces TPZ5534.

    The function completes JSON parsing before calling JSON.decode<T>. A malformed document returns an error string containing the parse cause, line and column. It never calls the decoder on a malformed or trailing input.

    After parsing succeeds, the selected decoder is called once. Its Ok payload or Err message becomes the result. Custom decoder effects occur after parsing and follow ordinary function evaluation. Built in decoding performs no I/O.

    The JSON protocol defines supported representations. Derived records ignore unknown fields and use declared defaults for missing fields. A missing required field, wrong kind, unknown enum tag, wrong payload count or value outside the target numeric range returns Err. No string to number or string to boolean coercion is performed.

    Built in errors describe the expected shape and first failing path rooted at $. Arrays are checked in increasing index order and object fields in ascending Unicode scalar order. Built in int decoding requires an exactly integral value within signed 64 bit bounds. Float decoding follows the protocol rounding and overflow rules. Optional null and nested option normalization follow the same protocol rule as JSON.decode. Use numberText and asInt when the input must retain the integer spelling boundary.

    Decode an already parsed tree with JSON.decode<T>. There is no second JSONValue receiver decoding form. Parsing failure and decoding failure are recoverable Result errors and do not produce assertion diagnostics by themselves.

    Связанное правило · Parse text before typed JSON decoding →

    Результат

    Дополнительные контракты не определены.

    The declared result type is Result<T, string>.

    Эффекты

    Не определено

    Ошибки

    Не определено

    Result and effects

    Ссылка

    Parse a complete JSON document before invoking the requested JSON decoder.

    Related entries

    Ссылка

    std.json →

    Parse text before typed JSON decoding

    Ссылка
    Правилоtopaz.stdlib.contract.json-parse-as.rule

    Parse text before typed JSON decoding

    parseAs<T> requires an explicit JSON decodable result type. The ordinary JSON capability checks apply. Omitting a required result type or selecting a type without decoding support produces TPZ5534.

    The function completes JSON parsing before calling JSON.decode<T>. A malformed document returns an error string containing the parse cause, line and column. It never calls the decoder on a malformed or trailing input.

    After parsing succeeds, the selected decoder is called once. Its Ok payload or Err message becomes the result. Custom decoder effects occur after parsing and follow ordinary function evaluation. Built in decoding performs no I/O.

    The JSON protocol defines supported representations. Derived records ignore unknown fields and use declared defaults for missing fields. A missing required field, wrong kind, unknown enum tag, wrong payload count or value outside the target numeric range returns Err. No string to number or string to boolean coercion is performed.

    Built in errors describe the expected shape and first failing path rooted at $. Arrays are checked in increasing index order and object fields in ascending Unicode scalar order. Built in int decoding requires an exactly integral value within signed 64 bit bounds. Float decoding follows the protocol rounding and overflow rules. Optional null and nested option normalization follow the same protocol rule as JSON.decode. Use numberText and asInt when the input must retain the integer spelling boundary.

    Decode an already parsed tree with JSON.decode<T>. There is no second JSONValue receiver decoding form. Parsing failure and decoding failure are recoverable Result errors and do not produce assertion diagnostics by themselves.

    Причина

    Parsing and decoding are separate boundaries. A complete syntax check prevents a user decoder from acting on malformed input, and one protocol dispatch keeps text and tree conversion consistent.

    Примеры Decode a record after parsing and report invalid data →Call a custom decoder once after complete parsing →

    Decode a record after parsing and report invalid data

    Ссылка

    run · running · Проверка · Не выполнялось

    main.tpzDecode a record after parsing and report invalid dataОткрыть песочницу →
    1. import std.json
    2. import std.test
    3. import std.io
    4. record Item derives JSON { name: string, count: int = 7 }
    5. let item = test.assertOk(json.parseAs<Item>("\{\"name\":\"ink\",\"extra\":true\}"))
    6. io.writeLine("{item.name},{item.count}")
    7. for text in (["\{\}", "17", "[", "\{\"name\":\"ink\",\"count\":9223372036854775808\}"]) {
    8. match (json.parseAs<Item>(text)) {
    9. case Ok(_) => io.writeLine("accepted")
    10. case Err(_) => io.writeLine("invalid data")
    11. }
    12. }
    Ожидаемый выводКод завершения 0
    ink,7
invalid data
invalid data
invalid data
invalid data
    $ topaz run main.tpz · Целевой продукт 5.21.3
    Ожидаемый результат

    Ожидаемый результат

    Выполнение завершается. Код завершения 0.

    Нет вывода ошибок.

    Ожидаемый стандартный вывод
    1. ink,7
    2. invalid data
    3. invalid data
    4. invalid data
    5. invalid data

    Этот пример ещё не выполнялся.

    Call a custom decoder once after complete parsing

    Ссылка

    run · running · Проверка · Не выполнялось

    main.tpzCall a custom decoder once after complete parsingОткрыть песочницу →
    1. import std.json { JSONValue, parseAs }
    2. import std.io
    3. record Token { text: string }
    4. impl JSON<Token> {
    5. function encode(value: Token) -> Result<JSONValue, string> {
    6. JSON.encode(value.text)
    7. }
    8. function decode(value: JSONValue) -> Result<Token, string> {
    9. io.writeLine("decode")
    10. match (value.asString()) {
    11. case Some(text) => Ok(Token { text: text })
    12. case None() => Err("expected token string")
    13. }
    14. }
    15. }
    16. match (parseAs<Token>("\"ink\"")) {
    17. case Ok(value) => io.writeLine(value.text)
    18. case Err(message) => io.writeLine(message)
    19. }
    20. match (parseAs<Token>("\"ink\" false")) {
    21. case Ok(_) => io.writeLine("accepted")
    22. case Err(_) => io.writeLine("parse failed before decode")
    23. }
    Ожидаемый выводКод завершения 0
    decode
ink
parse failed before decode
    $ topaz run main.tpz · Целевой продукт 5.21.3
    Ожидаемый результат

    Ожидаемый результат

    Выполнение завершается. Код завершения 0.

    Нет вывода ошибок.

    Ожидаемый стандартный вывод
    1. decode
    2. ink
    3. parse failed before decode

    Этот пример ещё не выполнялся.

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