Memory-managed wrapper type.

Construct a Once struct initialized to zero.

A convenience alias for Nothing :: Maybe Once.

Function to be called when starting a critical initialization section. The argument location must point to a static 0-initialized variable that will be set to a value other than 0 at the end of the initialization section. In combination with onceInitLeave and the unique address valueLocation, it can be ensured that an initialization section will be executed only once during a program's life time, and that concurrent threads are blocked until initialization completed. To be used in constructs like this:

C code

 static gsize initialization_value = 0;

 if (g_once_init_enter (&initialization_value))
   {
     gsize setup_value = 42; // initialization code here

     g_once_init_leave (&initialization_value, setup_value);
   }

 // use initialization_value here

Since: 2.14

Counterpart to onceInitEnter. Expects a location of a static 0-initialized initialization variable, and an initialization value other than 0. Sets the variable to the initialization value, and releases concurrent threads blocking in onceInitEnter on this initialization variable.

Since: 2.14

Set the value of the “retval” field to Nothing. When overloading is enabled, this is equivalent to

clear #retval

Get the value of the “retval” field. When overloading is enabled, this is equivalent to

get once #retval

Set the value of the “retval” field. When overloading is enabled, this is equivalent to

set once [ #retval := value ]

Get the value of the “status” field. When overloading is enabled, this is equivalent to

get once #status

Set the value of the “status” field. When overloading is enabled, this is equivalent to

set once [ #status := value ]