As I understand the let keyword introduces an immutable variable, so you can't
change it after initialization.
So for example
let x = @[1,2,3]
x[0] = 5
Run
wouldn't work.
Yesterday I discovered the library neo, which can be used to create matrices
and vectors. But there are some weird behaviors with the let keyword.
let
mm = ones(2, 2)
var
mb = mm[0..<2, 0..<2] # shares memory
mb[1,1] = 0.8
Run
mm is created as immutable matrix which contains only ones. So it shouldn't be
possible to change values in this matrix. When I'm trying to change a value of
mm for example with `mm[0,0] = 2` it doesn't work, which is expected.
But then 2 questions. First, the mb variable creates a slice of the matrix and
is declared as var. A slice in this library creates a reference to the
underlying array. Tho I'm able to change values of the original immutable
matrix. Shouldn't it be impossible to change a value of an immutable variable,
even if I create an immutable reference to it?
Then second question. The library contains two methods to get a row or a column
of the matrix:
let
mr = mm.row(0) # shares memory
mc = mm.column(0) # shares memory
mr[0] = 2
mc[1] = 3
Run
The variables mr and mc are immutable and they share the memory of an immutable
matrix. And I'm still able to change their values.
After executing this code and printing mm it results into `[[2, 1, 3, 0.8]]`.
Can someone explain this behavior to me?
