Array expanding

Timon Gehr timon.gehr at
Sun Dec 18 14:17:01 PST 2011

On 12/18/2011 11:12 PM, RenatoL wrote:
> Reading the book from Alexandrescu we can find this (page 103-104,
> at least in my edition):
> Expanding arrays has a couple of subtleties that concern possible
> reallocation of the array. Consider:
> auto a = [87, 40, 10, 2];
> auto b = a; // Now a and b refer to the same chunk
> a ~= [5, 17]; // Append to a
> a[0] = 15; // Modify a[0]
> assert(b[0] == 15); // Pass or fail?
> it seems natural that the test is ok but it is not... if we read
> more we find:
> "D leaves~= the freedom of either expanding by reallocation or
> opportunistically expanding in place if there is enough unused
> memory at the end of the current array."
> At a first glance this seems to be a serious issue... it seems hard
> to accept that b can lost its connection to "a" in a silent mode due
> to a reallocation
> Is there a safe mode to do this for large arrays?

Assuming 'safe' means preserving aliasing: No. How would you implement 
it? Anyway, this is not such a huge issue in practice. If you want 
aliasing, just don't append to the slices.

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