Swift Design: why array.endIndex is large than real lastest index and CGRect.maxY is same

Question

In the process of programming in swift, I encountered such a problem which confused me.

as shown in the picture above。

I found that the maxY property of CGRect is actually not included in CGRect. Because for a CGRect whose origin coordinate is (0, 0) and the length and width are 100, its actual maxY should be (0, 99).

I also found that the same problem exists in Array, for example, an array of [0, 1, 2, 3, 4, 5], his subscript should be 0-5, but the endIndex property of Array is 6.

I wonder why it is designed this way, does it make any sense?

Answer 1

Senario 1

CGRect.contains(_:) return true only if the coordinate is inside the rectangle or it is on the minimumX & minimumY edges.

If the point lies on the maximum edges it will return false.

In your case you are trying to check a point which lies on the maximum edge of the rect. So it will return ```false``.

Check the Documentation

A point is considered inside the rectangle if its coordinates lie inside the rectangle or on the minimum X or minimum Y edge.

Senario 2

endIndex of an array is defined as follows.

The array’s “past the end” position—that is, the position one greater than the last valid subscript argument.

So in your array,

5 is the last valid element which has the index of 5. So endIndex is defined as the 1 value higher than the index of the last element. So it will return 6.

Answer 2

CGRect.contains is actually refers CGRectContainsPoint . As the documentation says

A point is considered inside the rectangle if its coordinates lie inside the rectangle or on the minimum X or minimum Y edge.

So why?. Lets think we have a frame like CGRect(x: 0, y: 0, width: 3, height: 3)

What we expect that , We want a frame that x position is 0 and width must be 3.

From 0 to 3 Its like :

0->1->2->3

Numbers are point , arrows like feet

The distance is 3 yes but there is 4 points thats why Apple wants to eliminate 1 point. We can say that this is the last point from documentation. Thats why print(rect.contains(.init(x: 0, y: 0))) is true and print(rect.contains(.init(x: rect.maxX, y: rect.maxY))) or any other end point is not true