I don’t understand the following situation:
let a1: [[Double]] = [[1]]
let equ1 = a1 == a1 // This builds
let t1: (Double, Double) = (1, 1)
let equ2 = t1 == t1 // This builds also
let a2: [[(Double, Double)]] = [[(1,1)]]
let equ3 = a2 == a2 // This gives a build error
The build error is
Binary operator '==' cannot be applied to two '[[(Double, Double)]]' operands
Why can I check equality for a two-dim array of Double, for a tuple of 2 Doubles, but not for a two-dim array of this tuple?
It’s expected behavior. Let’s break down each case:
- Two-dimensional array
let a1: [[Double]] = [[1]]
let equ1 = a1 == a1
You’re comparing two-dimensional arrays of double, and since Double conformed to the Equatable protocol (== in this scenario), the array is fully conforming to the Equatable protocol too, which makes it able to compare. You may want to check this documentation.
- Tuple
let t1: (Double, Double) = (1, 1)
let equ2 = t1 == t1
SE-0015, Swift 2.2.1 indicates that you’re able to compare tuples up to 6 elements with the == function.
let t1: (Double, Double, Double, Double, Double, Double, Double) = (1, 1, 1, 1, 1, 1, 1)
let equ2 = t1 == t1 ❌
//Binary operator '==' cannot be applied to two '(Double, Double, Double, Double, Double, Double, Double)' operands
- Two-dimensional array of tuple
let a2: [[(Double, Double)]] = [[(1,1)]]
let equ3 = a2 == a2
Tuples are not able to conform to any kind of protocol until now. Even each element inside is able to do so, but that doesn’t mean the whole tuple can. I found this PR-46668 also asked the same question as you.
Site note: You may want to wrap it up into a Struct or Class, something like:
struct DoubleModel: Equatable {
let firstElement: Double
let secondElement: Double
}
let a3: [[DoubleModel]] = [[.init(firstElement: 1, secondElement: 1)]]
let equ3 = a3 == a3 ✅
0
Tuple as a type doesn’t conform to Equatable even if the elements does, the compiler has support for comparing tuples containing up to 6 elements for equality but that is not the same thing as conforming to the Equatable protocol.
And an Array object only conforms to Equatable if its elements does which isn’t the case here.
So neither your array of arrays of tuples or even a simple array of tuples will compare to Equatable out-of-the-box.