Unique

Encapsulates unique ownership of a resource.

When a Unique!T goes out of scope it will call destroy on the resource T that it manages, unless it is transferred. One important consequence of destroy is that it will call the destructor of the resource T. GC-managed references are not guaranteed to be valid during a destructor call, but other members of T, such as file handles or pointers to malloc memory, will still be valid during the destructor call. This allows the resource T to deallocate or clean up any non-GC resources.

If it is desirable to persist a Unique!T outside of its original scope, then it can be transferred. The transfer can be explicit, by calling release, or implicit, when returning Unique from a function. The resource T can be a polymorphic class object or instance of an interface, in which case Unique behaves polymorphically too.

If T is a value type, then Unique!T will be implemented as a reference to a T.

struct Unique (

) {

alias RefT = T;

version(None)

static Unique!T create(A args);

this(RefT p);

this(Unique!U u);

void opAssign(Unique!U u);

bool isEmpty [@property getter];

Unique release();

mixin Proxy!_p ;

this(this);

}

Constructors

this this(RefT p): Constructor that takes an rvalue. It will ensure uniqueness, as long as the rvalue isn't just a view on an lvalue (e.g., a cast). Typical usage:
this this(RefT p): Constructor that takes an lvalue. It nulls its source. The nulling will ensure uniqueness as long as there are no previous aliases to the source.
this this(Unique!U u): Constructor that takes a Unique of a type that is convertible to our type.

Destructor

A destructor is present on this object, but not explicitly documented in the source.

Postblit

this(this) this(this): Postblit operator is undefined to prevent the cloning of Unique objects.

Members

Aliases

RefT alias RefT = T: Represents a reference to T. Resolves to T* if T is a value type.

Functions

opAssign void opAssign(Unique!U u): Transfer ownership from a Unique of a type that is convertible to our type.
release Unique release(): Transfer ownership to a Unique rvalue. Nullifies the current contents. Same as calling std.algorithm.move on it.

Mixins

__anonymous mixin Proxy!_p: Forwards member access to contents.

Properties

isEmpty bool isEmpty [@property getter]: Returns whether the resource exists.

Static functions

create Unique!T create(A args): Allows safe construction of Unique. It creates the resource and guarantees unique ownership of it (unless T publishes aliases of this). Note: Nested structs/classes cannot be created.

Examples

struct S
{
    int i;
    this(int i){this.i = i;}
}
Unique!S produce()
{
    // Construct a unique instance of S on the heap
    Unique!S ut = new S(5);
    // Implicit transfer of ownership
    return ut;
}
// Borrow a unique resource by ref
void increment(ref Unique!S ur)
{
    ur.i++;
}
void consume(Unique!S u2)
{
    assert(u2.i == 6);
    // Resource automatically deleted here
}
Unique!S u1;
assert(u1.isEmpty);
u1 = produce();
assert(u1.i == 5);
increment(u1);
assert(u1.i == 6);
//consume(u1); // Error: u1 is not copyable
// Transfer ownership of the resource
consume(u1.release);
assert(u1.isEmpty);

The OpenD Programming Language