(x:y) operator in Julia

Question

I am trying to understand this code:

  r = (1:10) - (4/1)
    println(r)

Output:

-3.0:1.0:6.0

I understood why I got -3 and 6. But why I got that value in the middle (1.0)? How does Julia calculate it? Or how I can google it?

Answer 1

(first:step:last) syntax represent a Range type in Julia

typeof(1:10) # => UnitRange{Int32}

If step part is omitted, by default it is assumed 1

1:10 == 1:1:10 # => true

A Range is a compact view of a series

collect(1:10) # => 10-element Array{Int32,1}:
#  1
#  2
#  3
#  4
#  5
#  6
#  7
#  8
#  9
# 10

So it's expected that a Range type and a Vector follow the same rules e.g when you add a constant value like this:

collect(1+(1:10))==collect(1:10)+1 # => true

or even adding two vectors give you the same result of adding their range representation like this:

collect((1:10)+(1:10))==collect(1:10)+collect(1:10) # => true

Answer 2

The division operator in 4/1 returns a Float64. Although the original Range is a size 1 Int step Range, after adding a floating point to both sides it becomes a Float64 Range. As such, a step size of 1.0 is created by converting the implicit integer step size (floating point numbers are non-uniformly distributed, so uniform stepping is a little tricky - sometimes there are rounding issues).