a switch bug in swift? - "Switch must be exhaustive, consider adding a default clause."
<p>I am positive that the following <strong>swift</strong> code has covered all possibilities, but Xcode keeps telling me that, <strong>"Switch must be exhaustive, consider adding a default clause."</strong></p>

<p>Can anyone tell me what did I miss? Thanks.</p>

<pre><code>let a = false
let b = false
let c = false

func test(a: Bool, _ b: Bool, _ c: Bool) {
    switch (a, b, c) {
    case (true, false, _):
        print("Moved left!!!")
    case (true, true, _):
        print("Moved right!!!")
    case (false, _, false):
        print("Moved up!!!")
    case (false, _, true):
        print("Moved down!!!")
    // Error: Switch must be exhaustive, consider adding a default clause.
    }
}

test(false, false, false)
test(false, false, true)
test(false, true, false)
test(false, true, true)
test(true, false, false)
test(true, false, true)
test(true, true, false)
test(true, true, true)
</code></pre>