@inlinable
public subscript(index: Int) -> Element {
get {
// This call may be hoisted or eliminated by the optimizer. If
// there is an inout violation, this value may be stale so needs to be
// checked again below.
let wasNativeTypeChecked = _hoistableIsNativeTypeChecked()
// Make sure the index is in range and wasNativeTypeChecked is
// still valid.
let token = _checkSubscript(
index, wasNativeTypeChecked: wasNativeTypeChecked)
return _getElement(
index, wasNativeTypeChecked: wasNativeTypeChecked,
matchingSubscriptCheck: token)
}
_modify {
_makeMutableAndUnique() // makes the array native, too
_checkSubscript_native(index)
let address = _buffer.subscriptBaseAddress + index
yield &address.pointee
}
}
最近在swift源码中发现_modify { yield }
起初我以为是生成器
直到后面看到runtime/KeyPaths.cpp时才发现是下标访问相关的
写个测试类
class Test {
var vale = 0
public subscript(index: Int) -> Int {
get {
return 0
}
_modify {
yield &vale
}
}
}
let ctst = Test()
print(ctst.vale)
ctst[0] = 20
print(ctst.vale)
ctst[9] = 90
print(ctst.vale)
打印
image.png
