Optional arguments of subtype

General Usage
1

Hi good folks!
Quick question which I’m sure has been answered many times but which’s answers I can’t find.

Can I specify a subtype for an optional argument. Something similar to:

function f(a::Int64, b::T=10) where T<: MyOwnSpecialInt

If I can, what is the proper syntax? If not, why, and what is the proper way to do it instead?

2

That syntax works fine:

julia> f(a::Int, b::T=2) where T <: Real = a + b
f (generic function with 2 methods)

julia> f(1,2)
3

julia> f(1,2.0)
3.0

julia> f(1,2.0f1)
21.0f0

What error are you getting?

2 Likes
3

Thanks! I just realized my error.
In actuality I was trying to do

function f(a::Int64, b::T=OneOfMySpecialInts) where T<: MyOwnSpecialInt

But of course it should be

function f(a::Int64, b::Type{T}=OneOfMySpecialInts) where T<: MyOwnSpecialInt

Kind of classic mistake for me! While I love the multiple dispatch I’m not always friend with the syntax. :slight_smile:

1 Like