How does one trap arithmetic overflow errors in Swift?
Distinguish between an exception and a runtime error. An exception is thrown and can be caught. A runtime error stops your program dead in its tracks. Adding and getting an overflow is a runtime error, plain and simple. There is nothing to catch.
The point of an operator like &+
is that it doesn't error and it doesn't tell you there was a problem. That is the whole point.
If you think you might overflow, and you want to know whether you did, use static methods like addWithOverflow
. It returns a tuple consisting of the result and a Bool stating whether there was an overflow.
var x: Int8 = 100
let result = x &+ x // -56
x = 100
let result2 = Int8.addWithOverflow(x,x) // (-56, true)
Looks like this has become a non-static method in Swift 5, addingReportingOverflow(_:)
.
So for example,
UInt8.max.addingReportingOverflow(1)
will return (partialValue: 0, overflow: true)
See more on the Int
manual page
And of course the normal arithmetic operators that start with &
to allow overflow without returning overflow reports,
UInt8.max &+ 1
would return 0
as a UInt8