'+' is deprecated: Mixed-type addition is deprecated in Swift 3.1 - swift

Question

When I'm directly adding an integer value(i.e: 1,2,3,etc) with another integer variable
let arr:Array = ["One","Two"]
var valueT:Int64 = 0
value = arr.count + 1 //in this line
I get the following warning:
'+' is deprecated: Mixed-type addition is deprecated. Please use explicit type conversion.
I fixed it the warning with this:
value = Int64(value + 1)
Though it is fixed but I wanna know why its called Mixed-type addition as I didn't use ++ . Also is there a better way to fix the warning in swift 3.1?
Update:
The following image is the proof of warning. I'm using Xcode Version 8.3 (8E162).
allROR is an array here.

Answer 1

Edit: To generate the error with your code it should be like
let value = 5
let result: Int64 = value + 1
Now you get the warning
'+' is deprecated: Mixed-type addition is deprecated. Please use explicit type conversion.
But it is looks like warning is misleading, as of both value and 1 is of type Int so its summation also Int so you need to simply convert the result to Int64 and it is what you doing and that is perfectly ok.
let result: Int64 = Int64(value + 1)

Answer 2

Just to answer this part: why its called Mixed-type addition
With the simplified example by Nirav D:
let value = 5
let result: Int64 = value + 1
You can Command-click on + and see the generated interface of Collection:
(After Indexing has finished, of course.)
#available(swift, deprecated: 3.0, obsoleted: 4.0, message: "Mixed-type addition is deprecated. Please use explicit type conversion.")
public func +<T>(lhs: T.Stride, rhs: T) -> T where T : SignedInteger
So, in the code example above, the type of 1 is inferred as Int64, and as Int64.Stride == Int, the operation value + 1 matches the signature func +<T>(lhs: T.Stride, rhs: T) -> T where T : SignedInteger.
This deprecation is included in the revised version of SE-0104 Protocol-oriented integers, this part:
Standard Library no longer provides + and - operators for Strideable types.
They were problematic, as one could have written mixed-type code like
let x: Int64 = 42; x += (1 as Int), which would compile, but
shouldn't. Besides, since the Stride of an unsigned type is signed,
Standard Library had to implement a hack to make code like let x: UInt
= 42; x += (1 as Int) ambiguous. These operators were only necessary because they made advancing collection indices convenient, which is no
longer the case since the introduction of the new indexing model in
Swift 3.
As you already have seen, you can avoid this warning in many ways.

Answer 3

Data type is different that is why it is showing an error
you need to make both variable and constant of same data type
for e.g.
let result = value + Int64(1) //in this line

Answer 4

OK
var arr = [String]()
var i: Int64 = 0
if arr.count == 0 {
i = 1
} else {
i = arr.count + 1
}
gives as a warning '+' is deprecated: Mixed-type addition is deprecated. Please use explicit type conversion.
The reason is, that arr.count and i has different types. And this warning is right. It has nothing with the integer literal 1
this snippet gives you the warning too
var arr = [String]()
var i: Int64 = 0
if arr.count == 0 {
i = 1
} else {
i = 1
i += arr.count // here is the warning now
}
this will not compile, even though it looks very similar
var arr = [String]()
var i: Int64 = 0
if arr.count == 0 {
i = 1
} else {
let tmp = arr.count + 1
i = tmp
}
I hope we get an error message when we compose all of these snippets in the future release.