Update src/StructTypes.jl

Author: quinnj

src/StructTypes.jl

@@ -580,6 +580,8 @@ Base.haskey(s::SubTypeClosure, k::Symbol) = haskey(s._subtypes, k)
 Base.get(s::SubTypeClosure, k::Symbol, default)  = get(s._subtypes, k, s.f(k))
 Base.getindex(s::SubTypeClosure, k::Symbol) = get!(s, k, s.f(k))
 Base.get!(s::SubTypeClosure, k::Symbol, default) = get!(s._subtypes, k, s.f(k))
+# we hard-code length here because we still want to fulfill AbstractDict interface
+# but our closure approach is "lazy" in that we don't know subtypes until they're encountered
 Base.length(s::SubTypeClosure) = typemax(Int) 
 Base.keys(s::SubTypeClosure) = keys(s._subtypes)
 Base.values(s::SubTypeClosure) = values(s._subtypes)