invalid compiler error for generic function

[emekoi]

const std = @import("std");

pub fn Iterator(comptime T: type) type {
    return struct {
        const Self = @This();
        nextFn: fn next(self: *Self) ?T,
    };
}

pub fn StepBy(comptime T: type) type {
    return struct {
        parent: *Iterator(T),
        step: usize = 1,

        pub fn new(iter: *Iterator(T), n: usize) Iterator(T) {
            return StepBy(T){
                // .nextFn = undefined,
                .parent = iter,
                .step = n,
            };
        }
    };
}

test "iterator.StepBy" {
    _ = StepBy(usize).new(undefined, 9);
}

generates the error:

error: no member named 'parent' in struct 'Iterator(usize)'
                .parent = iter,

but

const std = @import("std");

pub fn Iterator(comptime T: type) type {
    return struct {
        const Self = @This();
        nextFn: fn next(self: *Self) ?T,
    };
}

pub fn StepBy(comptime T: type) type {
    return struct {
        parent: *Iterator(T),
        step: usize = 1,

        pub fn new(iter: *Iterator(T), n: usize) Iterator(T) {
            return StepBy(T){
                .nextFn = undefined,
                // .parent = iter,
                // .step = n,
            };
        }
    };
}

test "iterator.StepBy" {
    _ = StepBy(usize).new(undefined, 9);
}

generates

error: no member named 'nextFn' in struct 'StepBy(usize)'
                .nextFn = undefined,

[nektro]

the latter example now results in error: expected type 'StepBy(usize)', found 'Iterator(usize)' which gets to the issue that the defined and actual return type do not match