f(x::MyType{T, S}) where (T || S) <: Foo?

[Jollywatt]

@cjwyett

…
f(x::MyType{Foo}) = 5
f(x::MyType{<:FooBarBaz, Foo} = 5 #!!Repeated code!!

If this is really the only problem, just use a union type:

const MyTypeFoo = Union{MyType{Foo},MyType{<:FooBarBaz,Foo}}

f(x::MyTypeFoo) = 5

(As originally suggested by @uniment!)

@uniment

For something a bit more automated, how about this?

julia> fooey = [:(MyType{$(fill(:(<:Any), n)...), Foo}) for n=0:4]
5-element Vector{Expr}:
 :(MyType{Foo})
 :(MyType{<:Any, Foo})
 :(MyType{<:Any, <:Any, Foo})
 :(MyType{<:Any, <:Any, <:Any, Foo})
 :(MyType{<:Any, <:Any, <:Any, <:Any, Foo})

julia> const FooTypes = eval(:(Union{$(fooey...)}))

Then you could do

f(x::FooTypes) = ...