func testFloor1() { func f(array: inout [Double]) { for i in 0..<array.count { array[i] = floor(array[i]) } } var array = [Double](repeating: 1, count: 3840*2160*4) measure { // 58ms f(array: &array) } } func testFloor2() { func f<T: FloatingPoint>(array: inout [T]) { for i in 0..<array.count { array[i] = floor(array[i]) } } var array = [Double](repeating: 1, count: 3840*2160*4) measure { // 264ms f(array: &array) } }

floorがGenericかどうかで5倍も差がつく……