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Specification 6.0 · Not released · Tested product 5.21.3

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    Library · std.bytes

    Bytes.slice

    Returns a byte sequence selected by start and end positions.

    slice(start: int, end: int) -> Bytes
    Module
    std.bytes
    Receiver
    Bytes
    Minimum arity
    2
    Maximum arity
    2

    Declaration and parameters

    Link

    Availability

    Included by default: Pending

    Import std.bytes in language mode 5.21.

    The current compiler selects std/bytes.tpz for this language mode. Availability in other released editions and inclusion in each installed distribution are Pending.

    Source evidence

    Receiver

    Bytes

    Parameter constraints

    Additional contracts are Pending.

    Bytes.slice uses a start position and an exclusive end position measured in bytes.

    Valid bounds satisfy 0 <= start <= end <= length. The result contains exactly the bytes from start through end minus one.

    Equal endpoints produce empty Bytes, including endpoints at zero and at length. A full interval preserves every byte.

    Negative bounds, inverted bounds, and endpoints beyond length produce TPZ4001 at runtime. Bounds are not clamped or interpreted from the end.

    Slicing never changes the receiver. The receiver, start, and end expressions evaluate once in that order before the bounds are checked.

    A byte interval may split a UTF-8 encoding. Bytes.slice preserves those selected octets and Bytes.decodeUtf8 reports invalid text when they form an incomplete sequence.

    Related rule: Select explicit byte intervals

    Result

    Additional contracts are Pending.

    The declared result type is Bytes.

    Effects

    Pending

    Failures

    Pending

    Result and effects

    Link

    Copy the half-open interval from start to end. Invalid or inverted bounds produce TPZ4001 at runtime.

    Resolved contracts

    Link

    Related entries

    Link

    std.bytes

    Select explicit byte intervals

    Link
    Ruletopaz.stdlib.contract.bytes-slice.rule

    Select explicit byte intervals

    Bytes.slice uses a start position and an exclusive end position measured in bytes.

    Valid bounds satisfy 0 <= start <= end <= length. The result contains exactly the bytes from start through end minus one.

    Equal endpoints produce empty Bytes, including endpoints at zero and at length. A full interval preserves every byte.

    Negative bounds, inverted bounds, and endpoints beyond length produce TPZ4001 at runtime. Bounds are not clamped or interpreted from the end.

    Slicing never changes the receiver. The receiver, start, and end expressions evaluate once in that order before the bounds are checked.

    A byte interval may split a UTF-8 encoding. Bytes.slice preserves those selected octets and Bytes.decodeUtf8 reports invalid text when they form an incomplete sequence.

    Why

    An explicit interval should identify exactly the requested payload. Rejecting an invalid interval makes a mistaken byte count visible before subsequent decoding.

    Examples Select empty and nonempty intervalsKeep byte slicing separate from UTF-8 validationReject a negative slice startReject an inverted byte intervalReject an endpoint beyond the sequence

    Diagnostics TPZ4001

    Source evidence

    Select empty and nonempty intervals

    Link

    run · running · Verification: not-run

    main.tpzSelect empty and nonempty intervalsOpen in Playground
    1. import std.io
    3. let value = "abcd".encodeUtf8()
    4. io.writeLine(value.slice(0, 0).toHex())
    5. io.writeLine(value.slice(1, 3).toHex())
    6. io.writeLine(value.slice(4, 4).toHex())
    7. io.writeLine(value.toHex())
    Expected outputexit 0
    
6263

61626364
    $ topaz run main.tpz · target product 5.21.3
    Expected result

    Expected result

    Execution completes. Exit code 0.

    No stderr.

    Expected stdout
    2. 6263
    4. 61626364

    This exact example has not been executed.

    Source evidence

    Keep byte slicing separate from UTF-8 validation

    Link

    run · running · Verification: not-run

    main.tpzKeep byte slicing separate from UTF-8 validationOpen in Playground
    1. import std.io
    3. let byte = "é".encodeUtf8().slice(0, 1)
    4. io.writeLine(byte.toHex())
    5. match (byte.decodeUtf8()) {
    6. case Err(_) => io.writeLine("invalid UTF-8")
    7. case Ok(_) => io.writeLine("accepted")
    8. }
    Expected outputexit 0
    c3
invalid UTF-8
    $ topaz run main.tpz · target product 5.21.3
    Expected result

    Expected result

    Execution completes. Exit code 0.

    No stderr.

    Expected stdout
    1. c3
    2. invalid UTF-8

    This exact example has not been executed.

    Source evidence

    Reject a negative slice start

    Link

    run · running · Verification: not-run

    main.tpzReject a negative slice startOpen in Playground
    1. import std.bytes { Bytes }
    2. let value = "abcd".encodeUtf8()
    3. value.slice(-1, 2)
    Expected outputNonzero exit
    No stdout.
    $ topaz run main.tpz · target product 5.21.3
    Expected result

    Expected result

    Rejection during run. Nonzero exit.

    • TPZ4001 bytes-slice-bounds at main.tpz:3:1

    No stdout.

    This exact example has not been executed.

    Source evidence

    Reject an inverted byte interval

    Link

    run · running · Verification: not-run

    main.tpzReject an inverted byte intervalOpen in Playground
    1. import std.bytes { Bytes }
    2. let value = "abcd".encodeUtf8()
    3. value.slice(3, 2)
    Expected outputNonzero exit
    No stdout.
    $ topaz run main.tpz · target product 5.21.3
    Expected result

    Expected result

    Rejection during run. Nonzero exit.

    • TPZ4001 bytes-slice-bounds at main.tpz:3:1

    No stdout.

    This exact example has not been executed.

    Source evidence

    Reject an endpoint beyond the sequence

    Link

    run · running · Verification: not-run

    main.tpzReject an endpoint beyond the sequenceOpen in Playground
    1. import std.bytes { Bytes }
    2. let value = "abcd".encodeUtf8()
    3. value.slice(0, 5)
    Expected outputNonzero exit
    No stdout.
    $ topaz run main.tpz · target product 5.21.3
    Expected result

    Expected result

    Rejection during run. Nonzero exit.

    • TPZ4001 bytes-slice-bounds at main.tpz:3:1

    No stdout.

    This exact example has not been executed.

    Source evidence

    Diagnostics

    Link

    Index out of bounds

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