Component with Generic Type that has Generics Itself

[fabianboesiger]

Hi All,

I'm trying to construct something like this:

<Component<Vec<SomeType>> />

It seems that Leptos is unable to parse this. Is there any way to support this? A type alias appears to work, it is however not ideal.

[gbj]

You are correct that this does not parse in the view macro, and it is a limitation of the rstml crate we use for parsing the view macro.

There are definitely ways to support it; whether you like them or not are another question.

1. A type alias
2. Using a function, rather than a component, and calling it as a function (anywhere you can call a function, or in braces in the view)

#[component]
pub fn App() -> impl IntoView {
  view! {
    <p>"Some other content"</p>
    {Component::<Vec<String>>()}
  }
}

fn Component<T>() -> impl IntoView {}

3. Using a phantom type. Unless I'm mistaken, you can't have a generic component without using the prop anyway, for example as a PhantomData marker, so you can use that to provide the generic

#[component]
pub fn App() -> impl IntoView {
    view! {
      <Component marker={PhantomData::<Vec<String>>}/>
    }
}

#[component]
fn Component<T>(#[prop(optional)] marker: PhantomData<T>) -> impl IntoView {}

4. Making a PR to rstml to try to support the nested generic parsing (or a PR to leptos if it turns out the problem is here!)

[fabianboesiger]

Thanks for the reply, appreciate it!

The problem with the first and second approaches is that it isn't very ergonomic to do. The component will be in a crate provided to users who don't expect to require a type alias or use a function.

The problem with the third suggestion is that I use the type in a prop, but the prop is optional, so the type must be annotated in some cases.

I'll check out the rstml crate and see what I can do there.