Picking a Random Object in an NSArray

This is the simplest solution I could come up with:

id object = array.count == 0 ? nil : array[arc4random_uniform(array.count)];

It's necessary to check count because a non-nil but empty NSArray will return 0 for count, and arc4random_uniform(0) returns 0. So without the check, you'll go out of bounds on the array.

This solution is tempting but is wrong because it will cause a crash with an empty array:

id object = array[arc4random_uniform(array.count)];

For reference, here's the documentation:

u_int32_t
arc4random_uniform(u_int32_t upper_bound);

arc4random_uniform() will return a uniformly distributed random number less than upper_bound.

The man page doesn't mention that arc4random_uniform returns 0 when 0 is passed as upper_bound.

Also, arc4random_uniform is defined in <stdlib.h>, but adding the #import wasn't necessary in my iOS test program.

In Swift 4:

let array = ["one","two","three","four"]
let randomNumber = arc4random_uniform(UInt32(array.count))

array[Int(randomNumber)]