更改引用了动态数组的动态数组是一种不好的做法吗?

我看了一下D2中的动态数组,发现它们很难理解。看来我对说明书的解释也是错的。。 在更改数组时,处理动态数组的引用或切片似乎非常容易出错。。。或者我只是不了解基本原理?

引用同一数组仅共享实际项:

auto a = [1];
auto b = a;
assert(&a != &b); // different instance; Doesn't share length
assert(a.ptr == b.ptr); // same items
assert(a == [1]);
assert(a == b);

auto a = [1,2];
auto b = a;
a[1] = 20;
assert(a == [1,20]);
assert(a == b);

为了最大限度地提高效率,运行时总是尝试调整 如果新大小更大,并且阵列未通过 新操作员或以前的操作员

因此,更改长度并不一定会破坏参考:

auto a = [1];
auto b = a;
b.length = 2;
assert(b == [1,0]);
assert(a == [1]); // a unchanged even if it refers to the same instance
assert(a.ptr == b.ptr);  // but still the same instance

// So updates to one works on the other
a[0]  = 10;
assert(a == [10]);
assert(b == [10,0]);

从阵列上的规范

连接总是创建其操作数的副本,即使其中一个操作数是长度为0的数组

auto a = [1];
auto b = a;
b ~= 2; // Should make a copy, right..?
assert(a == [1]);
assert(b == [1,2]);
assert(a != b);
assert(a4.ptr == b.ptr); // But it's still the same instance
a[0] = 10;
assert(b == [10,2]); // So changes to a changes b

auto a = [1];
auto b = a;
b ~= 2;
assert(a == [1]);
assert(b == [1,2]);

a.length = 2; // Copies values to new memory location to not overwrite b's changes
assert(a.ptr != b.ptr);

在进行更改之前更改两个数组的长度会得到与上面相同的结果(我希望这是在上面给出的情况下):

auto a = [1];
auto b = a;
a.length = 2;
b.length = 2;
a[1] = 2;
assert(a == [1,2]);
assert(b == [1,0]);
assert(a.ptr != b.ptr);

当改变长度或癌变时也是如此(我希望这是鉴于上述情况):

auto a = [1];
auto b = a;
b.length = 2;
a ~= 2;
assert(a == [1,2]);
assert(b == [1,0]);
assert(a.ptr != b.ptr);

但随后切片也出现在画面中,突然变得更加复杂!切片可能是孤立的。。。

auto a = [1,2,3];
auto b = a;
auto slice = a[1..$]; // [2,3];
slice[0] = 20;
assert(a == [1,20,3]);
assert(a == b);

a.length = 4;
assert(a == [1,20,3,0]);
slice[0] = 200;
assert(b == [1,200,3]); // the reference to b is still valid.
assert(a == [1, 20, 3, 0]); // but the reference to a is now invalid..

b ~= 4;
// Now both references is invalid and the slice is orphan...
// What does the slice modify?
assert(a.ptr != b.ptr);
slice[0] = 2000;
assert(slice == [2000,3]);
assert(a == [1,20,3,0]); 
assert(b == [1,200,3,4]);

所以。。。对同一动态数组有多个引用是一种不好的做法吗?把片子传来传去。?或者我就在这里,错过了D中动态数组的全部要点?