a struct must have a `next()` method to be an iterator

Question

I get this error in vlang:

a struct must have a next() method to be an iterator

struct Items {
    item []Item
}

struct Item {
    name string
    link string
  tags []string
}

pub fn (mut app App) index() vweb.Result {
    text := os.read_file(app.db) or { panic(err) }
    items := json.decode(Items, text) or { panic(err) }
    println(items)
    return $vweb.html()
}

index.html:

@for item in items
    <h2>@item.name</h2>
@end

Answer 1

@DeftconDelta was looking in the right direction

You need to define a method called next that return an optional value (ie, that returns a type that starts with ? , for example, ?int .

So, for you this method would be something like the following:

// You need to include a pointer to the current item in your struct
struct Items {
    items       []Item
    current_idx int = -1
}

pub fn (mut i Items) next() ?Item {
    i.current_idx++
    if i.current_idx >= i.items.len {
        // tell the iterator that there are no more items
        return none
    }
    return i.items[i.current_idx]
}

Otherwise, if the struct isn't really necessary, you can just use an array of Item , so you don't have to bother with that

Answer 2

Disclaimer, this is my second day in V lang...

I got 1 step further with this added to stack.v , this is just my main.v file for this scenario

maybe you understand enough to keep you going after this stone step?

pub fn (i &Items) next() Item {
  return i.name
} 

it stopped complaining a struct must have a next() method to be an iterator

and started complaining about return types and insisting on an optional.

I was able to get this far thanks to: V Docs:ReferencesV Docs: Heap Structs V Docs: Methods V lib: Method Args

I look forward to hearing if this got you anywhere, I'll keep looking at this tomorrow because I want to understand it. But I been 'grammin 13hrs straight now, and I'll do better with a clear head...