Working with non-concrete types is often a problem for performance, so this approach may not be very efficient compared with alternatives that are more careful about the use of concrete types.
--John On Sunday, October 30, 2016 at 6:27:47 PM UTC-7, Ralph Smith wrote: > > Conversion is done by methods listed in base/nullable.jl > > I would like to know if there is any drawback to an alternative like > > abstract Bst > > immutable NullNode <: Bst end > > type BstNode <: Bst > val::Int > left::Bst > right::Bst > end > > isnull(t::Bst) = isa(t,NullNode) > > BstNode(key::Int) = BstNode(key, NullNode(), NullNode()) > > which appears to be good for type-safety, and is (sometimes) slightly > faster and less cumbersome than Nullables. > > On Sunday, October 30, 2016 at 6:24:42 PM UTC-4, Ángel de Vicente wrote: >> >> Hi, >> >> by searching in the web I found >> ( >> http://stackoverflow.com/questions/36383517/how-to-implement-bst-in-julia) >> >> a way to make my BST code much cleaner (as posted below). Nevertheless, >> I don't find this very ellegant, since the head node is of type Bst, >> while the children are of type Nullable{Bst} (is this the 'canonical' way >> of building recursive data structures with Julia?). >> >> But when I first read the code in SO, I thought that it was probably >> wrong, since it does: >> >> node.left = BST(key) >> where node.left is of type Nullable{BST}. >> >> Then I realized that automatic conversion from BST to Nullable{BST} is >> done when assigning to node.left, so all is good. Coming from Fortran, >> this is a bit odd for me... what are the rules for automatic conversion? >> >> >> >> Thanks a lot, >> Ángel de Vicente >> >> >> >> >> >> ,---- >> | module b >> | >> | type Bst >> | val::Int >> | left::Nullable{Bst} >> | right::Nullable{Bst} >> | end >> | Bst(key::Int) = Bst(key, Nullable{Bst}(), Nullable{Bst}()) >> | >> | "Given an array of Ints, it will create a BST tree, type: Bst" >> | function build_bst(list::Array{Int,1}) >> | head = list[1] >> | tree = Bst(head) >> | for e in list[2:end] >> | place_bst(tree,e) >> | end >> | return tree >> | end >> | >> | function place_bst(tree::Bst,e::Int) >> | if e == tree.val >> | println("Dropping $(e). No repeated values allowed") >> | elseif e < tree.val >> | if (isnull(tree.left)) >> | tree.left = Bst(e) >> | else >> | place_bst(tree.left.value,e) >> | end >> | else >> | if (isnull(tree.right)) >> | tree.right = Bst(e) >> | else >> | place_bst(tree.right.value,e) >> | end >> | end >> | end >> | >> | function print_bst(tree::Bst) >> | if !isnull(tree.left) print_bst(tree.left.value) end >> | println(tree.val) >> | if !isnull(tree.right) print_bst(tree.right.value) end >> | end >> | >> | end >> `---- >> >> ,---- >> | julia> include("bst.jl") >> | >> | julia> b.print_bst( b.build_bst([4,5,10,3,20,-1,10])) >> | Dropping 10. No repeated values allowed >> | -1 >> | 3 >> | 4 >> | 5 >> | 10 >> | 20 >> | >> | julia> >> `---- >> >> >> -- >> Ángel de Vicente >> http://www.iac.es/galeria/angelv/ >> >
