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move system_param fetch struct into anonymous scope to avoid name collisions (#4100)

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# Objective

avoid naming collisions with user structs when deriving ``system_param``.

## Solution

~rename the fetch struct created by ``#[derive(system_param)]`` from ``{}State`` to ``{}SysParamState``.~
place the fetch struct into an anonymous scope.

## Migration Guide

For code that was using a system param's fetch struct, such as ``EventReader``'s ``EventReaderState``, the fetch struct can now be identified via the SystemParam trait associated type ``Fetch``, e.g. for ``EventReader<T>`` it can be identified as ``<EventReader<'static, 'static, T> as SystemParam>::Fetch``
This commit is contained in:
robtfm 2022-05-02 18:26:50 +00:00
parent a011f4d53c
commit b9f738da8d
1 changed files with 39 additions and 35 deletions
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14
crates/bevy_ecs/macros/src/lib.rs
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@ -368,21 +368,24 @@ pub fn derive_system_param(input: TokenStream) -> TokenStream {
}));
let struct_name = &ast.ident;
let fetch_struct_name = Ident::new(&format!("{}State", struct_name), Span::call_site());
let fetch_struct_visibility = &ast.vis;
TokenStream::from(quote! {
// We define the FetchState struct in an anonymous scope to avoid polluting the user namespace.
// The struct can still be accessed via SystemParam::Fetch, e.g. EventReaderState can be accessed via
// <EventReader<'static, 'static, T> as SystemParam>::Fetch
const _: () = {
impl #impl_generics #path::system::SystemParam for #struct_name #ty_generics #where_clause {
type Fetch = #fetch_struct_name <(#(<#field_types as #path::system::SystemParam>::Fetch,)*), #punctuated_generic_idents>;
type Fetch = FetchState <(#(<#field_types as #path::system::SystemParam>::Fetch,)*), #punctuated_generic_idents>;
}
#[doc(hidden)]
#fetch_struct_visibility struct #fetch_struct_name<TSystemParamState, #punctuated_generic_idents> {
#fetch_struct_visibility struct FetchState <TSystemParamState, #punctuated_generic_idents> {
state: TSystemParamState,
marker: std::marker::PhantomData<fn()->(#punctuated_generic_idents)>
}
unsafe impl<TSystemParamState: #path::system::SystemParamState, #punctuated_generics> #path::system::SystemParamState for #fetch_struct_name<TSystemParamState, #punctuated_generic_idents> #where_clause {
unsafe impl<TSystemParamState: #path::system::SystemParamState, #punctuated_generics> #path::system::SystemParamState for FetchState <TSystemParamState, #punctuated_generic_idents> #where_clause {
fn init(world: &mut #path::world::World, system_meta: &mut #path::system::SystemMeta) -> Self {
Self {
state: TSystemParamState::init(world, system_meta),
@ -399,7 +402,7 @@ pub fn derive_system_param(input: TokenStream) -> TokenStream {
}
}
impl #impl_generics #path::system::SystemParamFetch<'w, 's> for #fetch_struct_name <(#(<#field_types as #path::system::SystemParam>::Fetch,)*), #punctuated_generic_idents> #where_clause {
impl #impl_generics #path::system::SystemParamFetch<'w, 's> for FetchState <(#(<#field_types as #path::system::SystemParam>::Fetch,)*), #punctuated_generic_idents> #where_clause {
type Item = #struct_name #ty_generics;
unsafe fn get_param(
state: &'s mut Self,
@ -413,6 +416,7 @@ pub fn derive_system_param(input: TokenStream) -> TokenStream {
}
}
}
};
})
}