On 06/10/2015 01:43 AM, Idan Arye wrote:
On Tuesday, 9 June 2015 at 23:04:41 UTC, Andrei Alexandrescu wrote:
On 6/9/15 3:58 PM, Timon Gehr wrote:
On 06/09/2015 05:28 PM, Andrei Alexandrescu wrote:
Following the use of This in Algebraic
(https://github.com/D-Programming-Language/phobos/pull/3394), we can
apply the same idea to Tuple, thus allowing one to create
self-referential types with ease.
Consider:
// A singly-linked list is payload + pointer to list
alias List(T) = Tuple!(T, This*);
// A binary tree is payload + two children
alias Tree(T) = Tuple!(T, This*, This*);
// or
alias Tree(T) = Tuple!(T, "payload", This*, "left", This*, "right");
// A binary tree with payload only in leaves
alias Tree2(T) = Algebraic!(T, Tuple!(This*, This*));
Is there interest in this? Other application ideas to motivate the
addition?
Andrei
Well, the issue is with this kind of use case:
alias List(T)=Algebraic!(Tuple!(),Tuple!(T,This*));
So a list is either nothing, or a head and a tail. What is the problem
here? -- Andrei
The `This*` here is not mapped to `Algebraic!(Tuple!(),Tuple!(T,This*))`
- it's mapped to the closest containing tuple, `Tuple!(T,This*)`. This
means that the tail is not a list - it's a head and a tail. The list is
either empty or infinite.
Exactly. Probably it was confusing that I used a raw pointer and not
some kind of NonNull!T hack. Non-null was the intention.
