Can't understand if deallocation happens?

[Mike Parker via Digitalmars-d-learn]

On Sunday, 22 January 2017 at 15:59:47 UTC, Suliman wrote:
> On Sunday, 22 January 2017 at 15:51:01 UTC, Suliman wrote:
>>  	string str = "abc";
>>  	writeln(str.ptr);
>>  	str = "def";
>>  	writeln("last data: ", *(str.ptr));
>>  	writeln("old data: ", *(str.ptr-1)); // print nothing
>>  	writeln("old data: ", *(str.ptr-2)); // print c
>>
>> It's look like that there is some gap between data, because 
>> `d` minus 1 should be `c`, but `c` I am getting only if I am 
>> doing `-2`. Why?
>
> writeln("old data: ", cast(int)*(str.ptr-1));
>
> #old data: 0
>
> String is gaping by zero?? I thought they are continuously like
>
> abcdef
> ---↑
>
> Where `↑` is equal to `ptr`.

You have *two* distinct strings here. Why do you expect them to 
be sequential in memory? If you want them to be treated as one 
string, concatenate them.

auto s1 = "abc";
auto s2 = "def";
auto s3 = s1 ~ s2;