Append const to array
Yuxuan Shui via Digitalmars-d-learn
digitalmars-d-learn at puremagic.com
Tue Sep 20 17:04:04 PDT 2016
On Tuesday, 20 September 2016 at 22:38:33 UTC, Jonathan M Davis
wrote:
> On Tuesday, September 20, 2016 22:23:08 Yuxuan Shui via
> Digitalmars-d-learn wrote:
>> struct A {
>> ulong[] x;
>> }
>> struct B {
>> ulong x;
>> }
>> void main() {
>> B[] b;
>> const(B) xx = B(1);
>> b ~= xx; // Works
>>
>> A[] c;
>> const(A) yy = A([1]);
>> c ~= yy; // Does not
>> }
>>
>> What gives?
>
> const(A) means that the ulong[] inside is const(ulong[]). When
> yy is copied
> to be appended to c, it goes from const(A) to A, which means
> that
> const(ulong[]) would need to be sliced and and set to ulong[],
> which would
> violate const, because it would mean that the last element in c
> could mutate
> then elements of its x, which would then mutate the elements in
> yy.
>
> - Jonathan M Davis
That makes sense, thanks.
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