Re: struct constructors and destructors.

[via Digitalmars-d]

On Thursday, 20 July 2017 at 09:09:42 UTC, Danni Coy wrote:

On Thu, Jul 20, 2017 at 12:19 AM, SrMordred via Digitalmars-d < digitalmars-d@puremagic.com> wrote:

On Wednesday, 19 July 2017 at 14:09:32 UTC, SrMordred wrote:

On Wednesday, 19 July 2017 at 09:09:40 UTC, Stefan Koch wrote:

On Wednesday, 19 July 2017 at 07:48:28 UTC, Danni Coy wrote:

Is there a reason that the following code

struct Foo
{
    this (string name)
    { do_something(name); }

    ~this()
    { undo_something(); }
}

Foo foo = void;

void open()
{
    foo = Foo("test"); // <- this line
}

tries to OpAssign foo to itself then calls foo's destructor?

What happens is this.

void open()
{
  foo = () {
  Foo _tmp = Foo.__ctor("test");
  return _tmp;
  } ();
}

Hm, isnt that wrong?

If I destroy resources on the dtor, wouldn't it invalidate the resource

on the copy?
Also, C++ behaves differently

No Sorry, it behaves almost the same.

just in D ctor and dtor are not called on declaration even if you drop " =

void".

Is there a way to delay the initialisation of a struct?

void initialization + emplace:

struct Foo
{
    this (string name)
    { create_count++; }

    ~this()
    { destroy_count--; }
}

int create_count;
int destroy_count;
Foo foo = void;

void main()
{
    import std.stdio;
    import std.conv : emplace;

    writefln("this(string) ran %s times.", create_count);
    writefln("~this() ran %s times.", destroy_count);

    emplace(&foo, "test");
    writeln("--- emplace ---");

    writefln("this(string) ran %s times.", create_count);
    writefln("~this() ran %s times.", destroy_count);
}

this(string) ran 0 times.
~this() ran 0 times.
--- emplace ---
this(string) ran 1 times.
~this() ran 0 times.

https://is.gd/G06GvK