std.collection lets rename it into std,ridiculous.
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Mon Feb 20 08:34:20 PST 2012
On 2/20/12 10:13 AM, Daniel Murphy wrote:
> "H. S. Teoh"<hsteoh at quickfur.ath.cx> wrote in message
> news:mailman.666.1329752861.20196.digitalmars-d at puremagic.com...
>>> Won't this reallocate every time you pop an element and then push a
>>> new one?
>> Nope, it doesn't. That's the power of D slices. When you create a
>> dynamic array, the GC allocates a certain amount of memory, let's call
>> it a "page", and sets the array to point to the beginning of this
>> memory. When you append to this array, it simply uses up more of this
>> memory. No reallocation actually occurs until the page is used up, at
>> which point the GC allocates a larger page to store the array in.
>> This scheme means that this code is very efficient for small stacks,
>> because there's no repeated allocation/deallocation (which if you ever
>> played with malloc/free, you'd know are expensive), just updating a few
>> pointers. For large stacks, the reallocations only take place
>> occasionally, so even in that case performance is still pretty good.
> This is incorrect.
> T stack = new immutable(int)(20);
> stack ~= 3; // probably does it in place
> auto stack2 = stack; // take a slice of the full stack
> stack = stack[0..$-1]; // ok, take a slice
> stack ~= 7; // must reallocate to avoid overwriting immutable memory
> Try it out, it works the same with mutable elements.
Yah, assumeSafeAppend() needs to be used in the stack implementation. I
don't know how we can address this better.
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