Dan Abramov Dan Abramov - 8 months ago 37
Swift Question

Is there no default(T) in Swift?

I'm trying to port the Matrix example from Swift book to be generic.

Here's what I got so far:

struct Matrix<T> {
let rows: Int, columns: Int
var grid: T[]

init(rows: Int, columns: Int, repeatedValue: T) {
self.rows = rows
self.columns = columns

grid = Array(count: rows * columns, repeatedValue: repeatedValue)

func indexIsValidForRow(row: Int, column: Int) -> Bool {
return row >= 0 && row < rows && column >= 0 && column < columns

subscript(row: Int, column: Int) -> T {
get {
assert(indexIsValidForRow(row, column: column), "Index out of range")
return grid[(row * columns) + column]
set {
assert(indexIsValidForRow(row, column: column), "Index out of range")
grid[(row * columns) + column] = newValue

Note that I had to pass
repeatedValue: T
to the constructor.

In C#, I would have just used
which would be
for numbers,
for booleans and
for reference types. I understand that Swift doesn't allow
on non-optional types but I'm still curious if passing an explicit parameter is the only way, or if I there is some equivalent of


There isn't. Swift forces you to specify the default value, just like then you handle variables and fields. The only case where Swift has a concept of default value is for optional types, where it's nil (Optional.None).