let condition = false //crash
let condition = true //no crash

struct S: Differentiable{
    var a: Float = 9
    var b: Float = 3
    var c: [Float] = [2.2]
    
    mutating func changeMyself(){
        a += b * 3
        c = c + [a] // when 'condition' is false -> Precondition failed: + should receive gradient with count equal to sum of operand counts, but counts are: gradient 0, lhs 1, rhs 1
        
        if condition{
            a += c.differentiableReduce(0, +)
        }
    }
}


func insertVerbHere(s: S) -> Float{
    var s = s
    s.changeMyself()
    return s.a
}


let grad = valueWithGradient(of: insertVerbHere)
print(grad(S()))

//Separate bug:

//when condition is true:
//prints (value: 38.2, gradient: S.TangentVector(a: 1.0, b: 0.0, c: []))

//but should be 
//(value: 38.2, gradient: S.TangentVector(a: 2.0, b: 6.0, c: [1.0]))