Playground wrong output

Question

I wonder if this is playground bug or it's supposed to work like this:

var types = ["0", "1", "2"]      // ["0","1","2"]
    types += "3"                 // ["0","1","2","3"]
    types += ["4", "5"]          // ["0","1","2","3","4","5"]
    types[3..5] = ["34"]         // ["34"]

In my opinion in last line types should contain ["0","1","2","34","5"], however playground gives different output - written on the right.

I would consider that on the right we can see only last edited stuff, but in line 2&3 we can see whole types array.

In assistant editor I get [0] "34", while it should be [3] "34" and rest of array in my opinion.

Answer 1

The reason you are seeing only ["34"] after the types[3..<5] = ["34"] line is because the assignment operator = returns the value that has been assigned.

The other lines show the whole array because the += operator returns the result of the assignment.

Answer 2

var refers to the mutable content and also you'r re assigning the values to it .

types[] - new value at index , mean it shouldn't be concatenate .

For Ex :

var types = ["0", "1", "2"]
types += "5"
types += ["4", "5"]
types[3..5] = ["34"] // Here considering the index of 3..5 (3 & 4) as one index - Assigning a single value  and replaced with the value
types