What "first" & "second" are referring to is inconsistent

[iiYese]

This example shows just one instance of this. .with::<&X>().set_second_name("$x") being synonymous with .with_first_name::<&X>("$x") is confusing. In the prior "second" is referring to the name of second part of the pair but in the later "first" is referring to the type parameter not the name of the second part of the pair.

[Indra-db]

@iiYese I see what you mean. set_first and set_second are meant as isolated "builder" functions for the pair. I think ideally I'd like to keep first and second referring to the typed, generic parameter, but as you pointed out, it does conflict with those "isolated" functions where you're only setting one part of the pair. Hmm.

Any suggestions besides making first and second refer to the function input parameter? Any preferences?

[iiYese]

You could remove those APIs & use tuples to overload set et al?

impl EntityView {
    // ..
    
    fn set(input: impl IntoField) {
        // ..
    }
    
    fn add(input: impl IntoTag) {
        // ..
    }
}

trait IntoField {
    // maybe don't need the world param?
    fn id(self, world: &World) -> Entity;
}

impl<T: ComponentId> IntoField for T {
    // ..
}

impl<T: ComponentId> IntoField for (T, Entity) {
    // ..
}

impl<T: ComponentId> IntoField for (Entity, T) {
    // ..
}

impl<T: ComponentId, U: ComponentId> IntoField for (T, Id<U>) {
    // ..
}

impl<T: ComponentId, U: ComponentId> IntoField for (Id<T>, U) {
    // ..
}

trait IntoTag {
    // maybe don't need the world param?
    fn id(self, world: &World) -> Entity;
}

// Ik we can't check for ZSTs like this yet, just to illustrate
impl<T: ComponentId + ZST> IntoTag for Id<T> {
    // ..
}

impl<T: ComponentId + ZST> IntoTag for (Id<T>, Entity) {
    // ..
}

impl<T: ComponentId + ZST> IntoTag for (Entity, Id<T>) {
    // ..
}

impl<T: ComponentId + ZST> IntoTag for (Entity, Entity) {
    // ..
}

impl<T: ComponentId + ZST, U: ComponentId + ZST> IntoTag for (Id<T>, Id<U>) {
    // ..
}

// And any combinations I missed

struct Id<T: ComponentId> {
    _phantom: PhantomData<T>;
}

fn id<T: ComponentId>() -> Id<T> {
    Id { _phantom: PhantomData }
}

Then the api wouldn't have first, seconds.

entity.set((Eats { amount: 5 }, id::<Apples>()));

You should be able to use this to overload on &'static strs as well to remove "name" variants too.