Variadic method in Swift

Question

Objective C Code:

- (instancetype)initWithInts:(int32_t)int1, ... {
    va_list args;
    va_start(args, int1);
    unsigned int length = 0;
    for (int32_t i = int1; i != -1; i = va_arg(args, int)) {
        length ++;
    }
    va_end(args);
    ...
    ...
    return self;
}

This code is used to count the numbers of method's parameters.

Swift Code:

convenience init(ints: Int32, _ args: CVarArgType...) {
    var length: UInt = 0
    self.init(length: args.count)
    withVaList(args, { _ in
        // How to increase length' value in loop?
    })
}

What's the best practise to use withVaList to loop through the argument list with a CVaListPointer? Help is very appreciated.

Gabriele Petronella · Accepted Answer · 2016-04-19T09:41:09.277

3

How about just

convenience init(args: Int...) {
  return args.count
}

edited Apr 19 '16 at 09:41

answered Apr 19 '16 at 09:30

Gabriele Petronella

106,943
21
217
235

What if I need to access the index of element in va_list ? likes do something like `array[i++] = arg;` – Zigii Wong Apr 19 '16 at 09:34
you mean while looping? In that case you loop over `ints.enumerate()`, which gives you also the index. See http://stackoverflow.com/questions/24028421/swift-for-loop-for-index-element-in-array – Gabriele Petronella Apr 19 '16 at 09:36
Maybe `args`, rather than `ints`? – Zigii Wong Apr 19 '16 at 09:40

score 1 · Answer 2 · answered Apr 19 '16 at 10:00

1

convenience required init(args: Int32...) {

}

If you define your func parameter following by three dots ..., you will notice args is actually a [Int32] type.

So just do casting likes Array, i.e. args.count, for i in args.

answered Apr 19 '16 at 10:00

Zigii Wong

7,766
8
51
79

Variadic method in Swift

2 Answers2