C++/CX：Array and WriteOnlyArray parameters

翻译自MSDN文档：

C++/CX supports authoring function parameters whose type is a read/write array (Platform::Array) or a write-only array (Platform::WriteOnlyArray). You can't define a WriteOnlyArray array, but you can declare a function parameter type as WriteOnlyArray so that the Windows Runtime can efficiently pass an Array by reference.

C++/CX支持编写参数为可读写数组（Platform::Array）或者是只读数组（Platform::WriteOnlyArray）的函数。你不能定义一个只读数组，但是你能声明函数参数为只读数组，以便windows runtime能有效的通过引用来传递数组。

The following code fragment declares a read/write array of 10 integers, a function whose parameter is a read/write array, and a call to that function. Note that you can declare only 1-dimensional Array and WriteOnlyArray objects.

接下来的代码块声明了一个可读写的包含10个整数的数组，一个参数为可读写数组的函数，和这个函数的调用。记住你只能声明一维可读写数组和只读数组对象。

using namespace Platform;

Array<int>^ ai = ref new Array<int>(10);
for (int i = 0; i < ai->Length; i++) 
    ai[i] = i;

long MyFunc1(const Array<int>^ p1) {
    long sum = 0;
    for (int x = 0; x < p1->Length; x++) 
        sum += p1[x];
    return sum;
};

MyFunc1(Array<int>^ ai);

The following code fragment declares a function whose first parameter is a WriteOnlyArray<T>. The function is called by using an Array<T> object even though the function parameter type is WriteOnlyArray<T>.

接下来的代码块声明了一个函数，第一个参数为WriteOnlyArray<T>。尽管函数参数是WriteOnlyArray<T>，但是函数还是被用Array<T> 对象来调用。

using namespace Platform;

void MyFunc2(WriteOnlyArray<int>^ a, int* actual) {
    *actual = 0;
    if (ai->Length > 2) {
        a[0] = 0;
        a[1] = 1;
        *actual = 2;
    }
};

int main() { 
    int used = 0;
    auto ai = ref new Array<int>(5);
    MyFunc2(ai, &used); // Array<T>^ has an implicit conversion to WriteOnlyArray<T>^
    return used;
}