无法将不可变值作为 inout 参数传递：'pointee' 是一个 get-only 属性

Question

来自 the Apple Docs 的这段代码给我：

Cannot pass immutable value as inout argument: 'pointee' is a get-only property

import Foundation
import Darwin

extension sockaddr_storage {
    //...
    static func fromSockAddr<AddrType, ReturnType>(_ body: (_ sax: inout AddrType) throws -> ReturnType) rethrows -> (ReturnType, sockaddr_storage) {
        precondition(MemoryLayout<AddrType>.size <= MemoryLayout<sockaddr_storage>.size)
        // We need a mutable `sockaddr_storage` so that we can pass it to `withUnsafePointer(to:_:)`.
        var ss = sockaddr_storage()
        let result = try withUnsafePointer(to: &ss) {
            try [=12=].withMemoryRebound(to: AddrType.self, capacity: 1) {
                // Error: Cannot pass immutable value as inout argument: 'pointee' is a get-only property
                try body(&[=12=].pointee)
            }
        }
        return (result, ss)
    }
}

我找不到编译它的方法。

Answer 1

您只需要将 withUnsafePointer 更改为 withUnsafeMutablePointer。

之所以可行，是因为 withMemoryRebound 现在传入 UnsafeMutablePointer<T> 而不是 UnsafePointer<T>，因此您可以改变 pointee.

代码：

extension sockaddr_storage {
    //...
    static func fromSockAddr<AddrType, ReturnType>(_ body: (_ sax: inout AddrType) throws -> ReturnType) rethrows -> (ReturnType, sockaddr_storage) {
        precondition(MemoryLayout<AddrType>.size <= MemoryLayout<sockaddr_storage>.size)
        var ss = sockaddr_storage()
        let result = try withUnsafeMutablePointer(to: &ss) {
            try [=10=].withMemoryRebound(to: AddrType.self, capacity: 1) {
                try body(&[=10=].pointee)
            }
        }
        return (result, ss)
    }
}

无法将不可变值作为 inout 参数传递：'pointee' 是一个 get-only 属性

Cannot pass immutable value as inout argument: 'pointee' is a get-only property

sockets

darwin

swift