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    Library · Strings

    string.toInt

    Parse an optional leading minus sign and ASCII decimal digits as an int.

    toInt() -> Option<int>
    Receiver
    string
    Minimum arity
    0
    Maximum arity
    0

    Declaration and parameters

    Availability

    Included by default · yes

    These types are provided by the language. No module import is required.

    The declarations below describe the standard operations on built-in values.

    Receiver

    string

    Parameter constraints

    Additional contracts are Pending.

    string.toInt() returns Option<int>. It accepts an optional leading - followed by one or more ASCII digits 0 through 9, and no other characters.

    Leading zeros are accepted. -0 produces 0.

    Leading or trailing whitespace, a leading +, digit separators, radix prefixes, exponents, fractions and non-ASCII digits return None(). Empty text and a lone - also return None().

    A spelled value below -9223372036854775808 or above 9223372036854775807 returns None(). The call never faults for its text.

    Call trim() before toInt() when the input format allows surrounding whitespace.

    Related rule · Parse decimal integers with one spelling →

    Result

    Additional contracts are Pending.

    The declared result type is Option<int>.

    Effects

    Pending

    Failures

    Pending

    Result and effects

    Return None() for any other spelling and for a value outside the int range.

    Related entries

    Strings →

    Parse decimal integers with one spelling

    Ruletopaz.stdlib.contract.string-to-int.rule

    Parse decimal integers with one spelling

    string.toInt() returns Option<int>. It accepts an optional leading - followed by one or more ASCII digits 0 through 9, and no other characters.

    Leading zeros are accepted. -0 produces 0.

    Leading or trailing whitespace, a leading +, digit separators, radix prefixes, exponents, fractions and non-ASCII digits return None(). Empty text and a lone - also return None().

    A spelled value below -9223372036854775808 or above 9223372036854775807 returns None(). The call never faults for its text.

    Call trim() before toInt() when the input format allows surrounding whitespace.

    Why

    One number has one accepted spelling, as in BigInt and Decimal text parsing. Rejecting whitespace and a plus sign keeps malformed input visible to the program, so a reader of wire formats does not accept a value that its writer never produces.

    Examples Parse a minus sign and decimal digits →Return None() for other spellings and out-of-range values →Return None() for surrounding whitespace and a plus sign →

    Parse a minus sign and decimal digits

    run · running · Verification · not-run

    main.tpzParse a minus sign and decimal digitsOpen in Playground →
    1. import std.io
    3. function show(text: string) -> string {
    4. match (text.toInt()) {
    5. case Some(value) => "{value}"
    6. case None() => "none"
    7. }
    8. }
    10. for text in (["42", "-7", "007", "-0", "9223372036854775807", "-9223372036854775808"]) {
    11. io.writeLine("[{text}] {show(text)}")
    12. }
    Expected outputExit code 0
    [42] 42
[-7] -7
[007] 7
[-0] 0
[9223372036854775807] 9223372036854775807
[-9223372036854775808] -9223372036854775808
    $ topaz run main.tpz · Target product 5.21.3
    Expected result

    Expected result

    Execution completes. Exit code 0.

    No stderr.

    Expected stdout
    1. [42] 42
    2. [-7] -7
    3. [007] 7
    4. [-0] 0
    5. [9223372036854775807] 9223372036854775807
    6. [-9223372036854775808] -9223372036854775808

    This exact example has not been executed.

    Return None() for other spellings and out-of-range values

    run · running · Verification · not-run

    main.tpzReturn None() for other spellings and out-of-range valuesOpen in Playground →
    1. import std.io
    3. function show(text: string) -> string {
    4. match (text.toInt()) {
    5. case Some(value) => "{value}"
    6. case None() => "none"
    7. }
    8. }
    10. for text in (["", "-", "12a", "1_000", "0x10", "1e3", "١٢", "9223372036854775808", "-9223372036854775809"]) {
    11. io.writeLine("[{text}] {show(text)}")
    12. }
    Expected outputExit code 0
    [] none
[-] none
[12a] none
[1_000] none
[0x10] none
[1e3] none
[١٢] none
[9223372036854775808] none
[-9223372036854775809] none
    $ topaz run main.tpz · Target product 5.21.3
    Expected result

    Expected result

    Execution completes. Exit code 0.

    No stderr.

    Expected stdout
    1. [] none
    2. [-] none
    3. [12a] none
    4. [1_000] none
    5. [0x10] none
    6. [1e3] none
    7. [١٢] none
    8. [9223372036854775808] none
    9. [-9223372036854775809] none

    This exact example has not been executed.

    Return None() for surrounding whitespace and a plus sign

    run · running · Verification · not-run

    main.tpzReturn None() for surrounding whitespace and a plus signOpen in Playground →
    1. import std.io
    3. function show(text: string) -> string {
    4. match (text.toInt()) {
    5. case Some(value) => "{value}"
    6. case None() => "none"
    7. }
    8. }
    10. for text in ([" 12", "12 ", "+5"]) {
    11. io.writeLine("[{text}] {show(text)}")
    12. }
    Expected outputExit code 0
    [ 12] none
[12 ] none
[+5] none
    $ topaz run main.tpz · Target product 5.21.3
    Expected result

    Expected result

    Execution completes. Exit code 0.

    No stderr.

    Expected stdout
    1. [ 12] none
    2. [12 ] none
    3. [+5] none

    This exact example has not been executed.

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