futureAssigned()
The futureAssigned() function is provided to check whether a Future Type variable is assigned or not (i.e. has a nil or 'null value).
Future types are available in Oxygene only, but futureAssigned() can in practice be called from C# and Swift, as well.
Syntax:
method futureAssigned(expression): Boolean;
bool futureAssigned(expression);
func futureAssigned(_ expression) -> Bool
bool futureAssigned(expression);
In contrast to the regular assigned() function, futureAssigned() will not evaluate the future, or wait for it to be evaluated, but simply check if any future is referenced – if so, that future value might still turn out to be nil.
In essence:
futureAssigned()checks for the existence of a future.assigned()checks the actual future value of the variable.
For example:
property value: future String read nil; // declared somewhere
...
var x: future String := async nil;
var y: future String := async "Slow to Calculate";
var z: future String {:= nil};
if assigned(x) then
// waits for the future to calculate, if necessary, and the checks if its nil or has a value.
// which will be nil, so this block will not run
...
if assigned(y) then
// waits for the future to calculate, if necessary, and the checks if its nil or has a value
// which will be "Slow to Calculate", so this block will run
...
if assigned(z) then
// has no future to wait for, so it will be false
// this block will not run
...
if futureAssigned(x) then // check if x contains any future at all. it does.
// this runs
...
if futureAssigned(y) then // check if y contains any future at all. it does.
// this runs
...
if futureAssigned(z) then // check if y contains any future at all. it does not.
// this will not run
...
to do: translate to all 4 languages