Tuple vs Dictionary differences

Question

Can someone please explain what the major differences there are between Tuples and Dictionaries are and when to use which in Swift?

Answer 1

Tuples are fixed-length things. You can’t add an extra element to a tuple or remove one. Once you create a tuple it has the same number of elements – var t = (1,2) is of type (Int,Int). It can never become (1,2,3), the most you could do is change it to, say, (7,8). This is all fixed at compile-time.

You can access the elements via their numeric positions like this

t.0 + t.1  // with (1,2), would equal 3
t.0 = 7

Arrays are variable length: you can start with an array var a = [1,2], and then add an entry via a.append(3) to make it [1,2,3]. You can tell how many items with a.count. You can access/update elements via a subscript: a[0] + a[2] // equals 4

You can name the elements in tuples:

var n = (foo: 1, bar: 2)

Then you can use those names:

n.foo + n.bar  // equals 3

This doesn’t remove the ability to access them by position though:

n.0 + n.1  // equals 3 

But these names, once set, are fixed at compile time just like the length:

n.blarg  // will fail to compile

This is not the same as dictionaries, which (like arrays), can grow or shrink:

var d = [“foo”:1, “bar”:2]
d[“baz”] = 3; 
d[“blarg”] // returns nil at runtime, there’s no such element