• jmh530 (24/24) Jun 07 2016 I modified one of the first examples from
• Adam D. Ruppe (9/11) Jun 07 2016 It doesn't matter what heap it is on, you are just using a
• jmh530 (2/13) Jun 07 2016 Thanks for the reply!

jmh530 <john.michael.hall gmail.com> writes:

I modified one of the first examples from 
std.experimental.allocator to put a struct on the heap (below).

My sense is that putting it on the GC heap gives the struct 
reference semantics. I was struck by two things. First, I didn't 
have to use (*a).x, I could just use a.x. Also, when I assign a 
struct object to another instance, changes in the new one also 
effect the original.


import std.experimental.allocator;

struct A
{
	int x;
}

void main()
{
	A* a = theAllocator.make!A(42);

	assert((*a).x == 42);
	assert(a.x == 42);
	
	auto b = a;
	assert(b.x == 42);
	++b.x;
	assert(b.x == 43);
	assert(a.x == 43);
}

Adam D. Ruppe <destructionator gmail.com> writes:

On Tuesday, 7 June 2016 at 15:39:59 UTC, jmh530 wrote:
 My sense is that putting it on the GC heap gives the struct 
 reference semantics.

It doesn't matter what heap it is on, you are just using a 
pointer here.

Struct pointers in D will automatically dereference with a.x, so 
no need for the * there (in most cases), and assigning it to 
another pointer of course still points to the same object, so it 
will affect both.

If you want a copy, you can use a special method to allocate a 
new one or use auto a = *b; which will copy it to the stack.

jmh530 <john.michael.hall gmail.com> writes:

On Tuesday, 7 June 2016 at 15:43:34 UTC, Adam D. Ruppe wrote:
 On Tuesday, 7 June 2016 at 15:39:59 UTC, jmh530 wrote:
 My sense is that putting it on the GC heap gives the struct 
 reference semantics.

 It doesn't matter what heap it is on, you are just using a 
 pointer here.

 Struct pointers in D will automatically dereference with a.x, 
 so no need for the * there (in most cases), and assigning it to 
 another pointer of course still points to the same object, so 
 it will affect both.

 If you want a copy, you can use a special method to allocate a 
 new one or use auto a = *b; which will copy it to the stack.

Thanks for the reply!