Problem with insertBack

[ag0aep6g via Digitalmars-d-learn]

On 06/03/2016 04:34 PM, John Nixon wrote:
> import std.stdio;
> import std.container;
> struct CS{
>    char[] t;
>    CS dup()const{
>      CS cs;
>      cs.t = this.t.dup;
>      return cs;}
> };

Aside: No semicolon after struct declarations in D.

> void main(){
>    Array!CS cs_array = make!(Array!CS)();

cs_array stores its data somewhere on the heap.

>    CS cs;

cs is on the stack.

>    cs.t = "bb".dup;

But cs.t's data is on the heap, like cs_array's. cs.t contains a pointer 
to it.

>    cs_array.insertBack(cs);

This copies cs to cs_array's heap. The pointer in cs.t is being copied, 
but the data that it points to is not being copied. So cs.t and 
cs_array[0].t contain two distinct but equal pointers now. Since they're 
equal, they refer to the same data.

>    write("cs_array = ");foreach(i2;cs_array)write(i2);writeln("");
>    cs.t[0] = ("a".dup)[0];//this changes cs_array!

This is expected since cs.t and cs_array[0].t point to the same 
location. A change to the data through one of them is visible to the other.

>    write("cs_array = ");foreach(i2;cs_array)write(i2);writeln("");
>    cs.t = "c".dup;//but this does not

Here you're not writing through the pointer in cs.t, but rather you're 
assigning a whole new one. Since the pointers in cs.t and cs_array[0].t 
are independent of each other, they now point to different locations, 
with different data.

>    write("cs_array = ");foreach(i2;cs_array)write(i2);writeln("");
>    return;}