In Julia, why can "if false" statements in local scope modify function definitions?

Question

In Julia 1.4.1, if I define a function in a global scope, modifications after "if false" statements do not affect it, as expected:

test()=0
if false
  test()=1
end

println(test())

This prints "0", as it should. However, when I enclose this code within a local scope, the behavior changes:

function main()
  test()=0
  if false
    test()=1
  end

  println(test())
end

main()

This now prints "1" which I did not expect. If I change "test" to be an array or a float I observe no modification as expected, i.e. the problem does not occur. Why does Julia behave this way for functions?

user_176071 · Answer

The solution is to use anonymous functions in cases like this:

function main()
  test = () -> 0
  if false
    test = () -> 1
  end

  println(test())
end

julia> main()
0

As for the why, this gets to the core of what it means to define and redefine a particular method of a function.

In Julia, why can "if false" statements in local scope modify function definitions?

1 Answers