Julia variable disappears/changes

Question

I have the following MWE

function f(p)
  ans = zeros(p, 2)
  return ans
end

ans = f(2)

ans

b=ans.+1.0
ans

At first, ans is correct, but the operation creating b overwrites ans.

julia> ans = f(2)
2×2 Matrix{Float64}:
 0.0  0.0
 0.0  0.0

julia> ans
2×2 Matrix{Float64}:
 0.0  0.0
 0.0  0.0

julia> b=ans.+1.0
2×2 Matrix{Float64}:
 1.0  1.0
 1.0  1.0

julia> ans
2×2 Matrix{Float64}:
 1.0  1.0
 1.0  1.0

It's a fresh install of julia 1.6.5.

The same thing happens if I just ask typeof(ans). The value of ans itself changes to the output of typeof(ans) which is a DataType.

julia> ans=f(2)
2×2 Matrix{Float64}:
 0.0  0.0
 0.0  0.0

julia> typeof(ans)
Matrix{Float64} (alias for Array{Float64, 2})

julia> typeof(ans)
DataType

Any ideas?

Answer 1

See the docstring of ans:

help?> ans
  ans

  A variable referring to the last computed value, automatically set at the interactive prompt.

So as you can see Julia REPL automatically overwrites ans after each evaluation of an expression.

In short it is recommended not to use ans in a global scope in interactive sessions (except to get the result of last operation).