[swift-evolution] [Review] SE-0128: Change failable UnicodeScalar initializers to failable

王 黎明 uomb at outlook.com
Thu Jul 21 23:09:14 CDT 2016


Maybe off topic.

The problem is there’s no process for the validty of the parameter.

The source of UnicodeScala:

  public init(_ v: UInt32) {
    // Unicode 6.3.0:
    //     D9.  Unicode codespace: A range of integers from 0 to 10FFFF.
    //     D76. Unicode scalar value: Any Unicode code point except
    //     high-surrogate and low-surrogate code points.
    //     * As a result of this definition, the set of Unicode scalar values
    //     consists of the ranges 0 to D7FF and E000 to 10FFFF, inclusive.

    _precondition(v < 0xD800 || v > 0xDFFF,
        "high- and low-surrogate code points are not valid Unicode scalar values")
    _precondition(v <= 0x10FFFF, "value is outside of Unicode codespace")

    self._value = v

55357 == 0xD83D , not less than 0xD800

The _precondition like assert.

在 2016年7月22日,上午10:23,Karl via swift-evolution <swift-evolution at swift.org<mailto:swift-evolution at swift.org>> 写道:

+1. I was trying to build a naive random string generator the other day (but I wanted it to occasionally spit out extended clusters like emojis), and was also surprised that the initialiser crashes.

Could probably be filed under “bug fixes”, even.


On 22 Jul 2016, at 00:28, Chris Lattner via swift-evolution <swift-evolution at swift.org<mailto:swift-evolution at swift.org>> wrote:

Hello Swift community,

The review of "SE-0128: Change failable UnicodeScalar initializers to failable" begins now and runs through July 24. The proposal is available here:


Reviews are an important part of the Swift evolution process. All reviews should be sent to the swift-evolution mailing list at


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