Question

作为参数传递时，

UnsafeRawPointers can be implicitly cast到var x = 42 func print<T>(address p: UnsafeRawPointer, as type: T.Type) { print(p.load(as: type)) } withUnsafePointer(to: &x) { (ptr) in print(address: ptr, as: Int.self) // Prints "42" }：

UnsafeBufferPointer

但是，似乎UnsafeRawBufferPointer无法隐式转换为var x = 42 func printBuffer<T>(address p: UnsafeRawBufferPointer, as type: T.Type) { print(p.load(as: type)) } withUnsafePointer(to: &x) { (ptr) in let buff = UnsafeBufferPointer(start: ptr, count: 1) printBuffer(address: buff, as: Int.self) // 1 }：

// 1

在此代码段中，标有create or replace function array_unique_elements(arr anyarray) returns integer language sql immutable as $$ select count(distinct a)::int from unnest(arr) a $$;错误的行：

无法转换类型＆＃39; UnsafeBufferPointer＆＃39;预期参数类型＆＃39; UnsafeRawBufferPointer＆＃39;

为什么在允许前一个隐式转换时不可能进行隐式转换？

Answer 1

你不能施放 UnsafeBufferPointer到UnsafeRawBufferPointer 因为这不仅仅是重新解释指针：它需要计算原始字节数。

但您可以<{1}} 创建 UnsafeRawBufferPointer：

UnsafeBufferPointer

以下是UnsafeRawBufferPointer.swift.gyb中初始值设定项的实现：

withUnsafePointer(to: &x) { (ptr) in
    let buff = UnsafeBufferPointer(start: ptr, count: 1)
    let rawBuff = UnsafeRawBufferPointer.init(buff)
    printBuffer(address: rawBuff, as: Int.self)
}

从UnsafeBufferPointer到UnsafeRawBufferPointer的隐式转换

1 个答案: