> But I think your confusion is more about how what a compiler means by pointer type, and what a human means. If you pull away enough layers of abstraction, the compiler doesn't see *Type it'll only see *anyopaque, phrased completely differently; according to the compiler, all pointers are the same and are exactly memory_address_size() big. *Type doesn't really exist.
Check out the implementation of SinglyLinkedList in the latest release (before the change in the post)[0]. You'll notice the argument for SinglyLinkedList is (comptime T: type), which is used in the internal Node struct for the data field, which is of type T. Notably, the data field is not a *T.
In Zig, when you call the function SinglyLinkedList with the argument i32 (like SinglyLinkedList(i32)) to return a type for a list of integers, the i32 is used in the place of T, and a Node struct that is unique for i32 is defined and used internally in the returned type. Similarly, if you had a struct like Person with fields like name and age, and you created a list of Persons like SinglyLinkedList(Person), a new Node type would be internally defined for the new struct type returned for Person lists. This internal Node struct would instead use Person in place of T. The memory for the Node type used internally in SinglyLinkedList(Person) actually embeds the memory for the Person type, rather than just containing a pointer to a Person.
These types are very much known to the compiler, as the layout of a Node for a SinglyLinkedList(i32) is not the same as the layout of a Node for a SinglyLinkedList(Person), because the argument T is not used as a pointer. Unless, as the gp mentioned, T is explicitly made to be a pointer (like SinglyLinkedList(*Person)).
Check out the implementation of SinglyLinkedList in the latest release (before the change in the post)[0]. You'll notice the argument for SinglyLinkedList is (comptime T: type), which is used in the internal Node struct for the data field, which is of type T. Notably, the data field is not a *T.
In Zig, when you call the function SinglyLinkedList with the argument i32 (like SinglyLinkedList(i32)) to return a type for a list of integers, the i32 is used in the place of T, and a Node struct that is unique for i32 is defined and used internally in the returned type. Similarly, if you had a struct like Person with fields like name and age, and you created a list of Persons like SinglyLinkedList(Person), a new Node type would be internally defined for the new struct type returned for Person lists. This internal Node struct would instead use Person in place of T. The memory for the Node type used internally in SinglyLinkedList(Person) actually embeds the memory for the Person type, rather than just containing a pointer to a Person.
These types are very much known to the compiler, as the layout of a Node for a SinglyLinkedList(i32) is not the same as the layout of a Node for a SinglyLinkedList(Person), because the argument T is not used as a pointer. Unless, as the gp mentioned, T is explicitly made to be a pointer (like SinglyLinkedList(*Person)).
[0] https://ziglang.org/documentation/0.14.0/std/#src/std/linked...