On Friday, 10 February 2023 at 22:10:20 UTC, Ben Jones wrote:
I'm trying to write a range adaptor for linked list types. The
range type seems to work OK, but my helper function to deduce
the node type has a compiler error. My hunch is that
`nextField` loses its association with T when I'm trying to
pass it as a template parameter inside the helper method, but I
can't use __traits(child) there to fix it.
Any idea how to fix the helper method?
As a workaround, you can use a `string` instead of an `alias`:
```diff
--- before.d 2023-02-11 01:48:08.922945736 -0500
+++ after.d 2023-02-11 01:47:42.062922019 -0500
@@ -1,7 +1,7 @@
import std.stdio;
import std.range;
-struct LinkedListAdaptor(alias nextField, T){
+struct LinkedListAdaptor(string nextField, T){
T current;
@safe:
nothrow:
@@ -19,11 +19,11 @@
}
void popFront() {
- current = __traits(child, current, nextField);
+ current = __traits(getMember, current, nextField);
}
}
-auto linkedListAdaptor(alias nextField, T)(T head) if(is(T ==
U*, U)){
+auto linkedListAdaptor(string nextField, T)(T head) if(is(T ==
U*, U)){
return LinkedListAdaptor!(nextField, T)(head);
//fails with:
@@ -39,8 +39,8 @@
void main(){
Node* head = new Node(10, new Node(20, null));
- auto rng1 = LinkedListAdaptor!(Node.next, Node*)(head);
- auto rng = linkedListAdaptor!(Node.next)(head);
+ auto rng1 = LinkedListAdaptor!("next", Node*)(head);
+ auto rng = linkedListAdaptor!("next")(head);
foreach(const x; rng){
writeln(x.data);
}
```
