Dynamic Arrays as Stack and/or Queue

[mipri]

On Monday, 7 October 2019 at 19:16:31 UTC, IGotD- wrote:
> On Monday, 7 October 2019 at 17:36:09 UTC, Ferhat Kurtulmuş 
> wrote:
>>>
>>> I'm not talking about memory deletion. I'm talking about 
>>> push, pop, enqueue, and dequeue behavior. I'd assume in a 
>>> garbage collected language letting the reference float off 
>>> should be picked up by the GC.
>> I'm sorry. Writing on my mobile phone. Maybe this is what you 
>> are looking for
>> https://dlang.org/phobos/std_container_dlist.html
>
> I think what he is looking for are the general pop_front, 
> push_front, pop_back and push_back that you would find in 
> virtually any C++ STL container algorithms like list, vector or 
> map.
>
> I think this is a good question as I don't really see any good 
> example in the documentation of the dynamic arrays about this. 
> This is very common use case for arrays. Is there any D 
> equivalent?

With the performance that you'd expect, I believe:

#! /usr/bin/env rdmd
import std.stdio;
import std.algorithm : moveAll;

void push_front(T)(ref T[] xs, T x) {
     ++xs.length;
     moveAll(xs[0 .. $-1], xs[1..$]);
     x[0] = x;
}
T pop_front(T)(ref T[] xs) {
     T x = xs[0];
     moveAll(xs[1 .. $], xs[0 .. $-1]);
     --xs.length;
     return x;
}
void push_back(T)(ref T[] xs, T x) {
     xs ~= x;
}
T pop_back(T)(ref T[] xs) {
     T x = xs[$ - 1];
     --xs.length;
     return x;
}

void main() {
     int[] xs;
     foreach (i; 0 .. 10)
         xs.push_back(i);
     writeln(xs.pop_back());  // output: 9
     writeln(xs.pop_front()); // output: 0
     writeln(xs.pop_front()); // output: 1
     writeln(xs); // output: [2, 3, 4, 5, 6, 7, 8]
}