Update this statement for Julia 1.0

Question

Could someone explain how to update this for Julia 1.0

function _encode_zigzag{T <: Integer}(n::T)
    num_bits = sizeof(T) * 8
    (n << 1) ⊻ (n >> (num_bits - 1))
end

And also what is the difference with:

function _encode_zigzag(n::Integer)
    num_bits = sizeof(T) * 8
    (n << 1) ⊻ (n >> (num_bits - 1))
end

Answer 1

Firstly, in Julia 1.x the subtype constraints on type parameters are stated after the parameters and followed by the reserved word where.

function _encode_zigzag(n::T) where {T <: Integer}
    num_bits = sizeof(T) * 8
    (n << 1) ⊻ (n >> (num_bits - 1))
end

The curly braces are unnecessary when there is only one type parameter but it is recommended to keep for clarity.

Now for the second question. In the version of your method where n is an Integer, sizeof will not work since the size of an abstract type is undefined. In this case, establishing the subtype constraint helps make sure that the given argument will have a defined size while still giving flexibility for different types. Julia will compile different versions of the function; one for each Integer subtype that gets passed.

This is more efficient than declaring the function with n having a concrete type like Int64, since this would mean the argument would have to be converted to the same type before executing the function.

You can read more of this in the Julia documentation.