Basic Operators

Unlike C, Swift lets you perform remainder (%) calculations on floating-point numbers.

if x = y {
    // this is not valid, because x = y does not return a value
}

// Swift中的取模操作
-9 % 4   // equals -1，理解成：-9 = (4 × -2) + -1

Swift also provides two identity operators (=== and !==), which you use to test whether two object references both refer to the same object instance

// ？？？
var arr1 = [1, 2, 3]
var arr2 = arr1
arr2[0] = 10;
arr1     // [10, 2, 3]
arr2     // [10, 2, 3]
arr1 === arr2  // 修改arr2，arr1也跟着修改，所以应该是指向一个object，这里应该是true，但结果却是false