From type/Supply

See Original text in context

method stable(Supply:D: $time, :$scheduler = $*SCHEDULER --> Supply:D)

Creates a new supply that only passes on a value flowing through the given supply if it wasn't superseded by another value in the given $time (in seconds). Optionally uses another scheduler than the default scheduler, using the :scheduler parameter.

To clarify the above, if, during the timeout $time, additional values are emitted to the Supplier all but the last one will be thrown away. Each time an additional value is emitted to the Supplier, during the timeout, $time is reset.

This method can be quite useful when handling UI input, where it is not desired to perform an operation until the user has stopped typing for a while rather than on every keystroke.

my $supplier = Supplier.new;
my $supply1 = $supplier.Supply;
$supply1.tap(-> $v { say "Supply1 got: $v" });
$supplier.emit(42);
 
my Supply $supply2 = $supply1.stable(5);
$supply2.tap(-> $v { say "Supply2 got: $v" });
sleep(3);
$supplier.emit(43);  # will not be seen by $supply2 but will reset $time 
$supplier.emit(44);
sleep(10);
# OUTPUT: «Supply1 got: 42␤Supply1 got: 43␤Supply1 got: 44␤Supply2 got: 44␤» 

As can be seen above, $supply1 received all values emitted to the Supplier while $supply2 only received one value. The 43 was thrown away because it was followed by another 'last' value 44 which was retained and sent to $supply2 after approximately eight seconds, this due to the fact that the timeout $time was reset after three seconds.