Struct WeakRef

Extremely simple intrusive weak reference implementation.

struct WeakRef(T)
  
if (isReferenceType!T && hasDestructionFlag!T);

WeakRef serves one task: to notice a dangling pointer after object destruction. For example, class A owns object B, and class C needs to temporarily save B. So C accepts WeakRef of B. If object A decides to destroy B, C will stay with null reference.

Object B must satisfy some requirements, because of intrusive nature of WeakRef. See example below.

Constructors

NameDescription
this (object) Create a weak reference. object must be valid, of course.

Fields

TypeNameDescription
T
 data
const(bool)*
 flag

Methods

NameDescription
get () Get the object reference
nullify () Set this reference to point nowhere
opCast () True if the object exists
opEquals (s) Allows to use WeakRef with destroyed item as key in associative arrays
toHash () Allows to use WeakRef with destroyed item as key in associative arrays

Limitations

WeakRef cannot forward custom opEquals and toHash calls, because their results need to be consistent before and after object destruction.

Example

class B
{
    bool* destructionFlag;

    this()
    {
        destructionFlag = new bool;
    }

    ~this()
    {
        *destructionFlag = true;
    }
}

WeakRef!B reference;
assert(!reference);

B b = new B;
reference = weakRef(b);

assert(b == reference.get);
assert(reference);

WeakRef!B ref2 = reference;
ref2.nullify();
assert(!ref2);

destroy(b);
assert(!reference);