system_for_each must be able to accept Entity as a component

zero_ecs_macros/src/system_for_each_impl.rs

@@ -8,10 +8,12 @@ use crate::query_impl::get_collection_component_fields;
 pub fn system_for_each(attr: TokenStream, item: TokenStream) -> TokenStream {
     let foreign_struct = syn::parse_macro_input!(attr as ItemStruct);
     let collection_component_fields = get_collection_component_fields(foreign_struct);
-    let component_types: HashSet<_> = collection_component_fields
+    let mut component_types: HashSet<_> = collection_component_fields
         .iter()
         .map(|ccf| &ccf.field_type)
         .collect();
+    let entity_name = "Entity".to_string();
+    component_types.insert(&entity_name);
     let input_fn = syn::parse_macro_input!(item as ItemFn);
 
     let fn_vis = &input_fn.vis;

zero_ecs_testbed/src/integration_tests/test_simple.rs

@@ -1,3 +1,5 @@
+use std::collections::HashSet;
+
 use zero_ecs::*;
 
 pub struct Value(usize);
@@ -76,3 +78,41 @@ fn can_make_mutable_query() {
     world.assert_value_for(0, b);
     world.assert_value_for(0, d);
 }
+
+struct ToDestroy(HashSet<Entity>);
+
+#[system_for_each(World)]
+pub fn destroy_even_values(entity: &Entity, value: &Value, to_destroy: &mut ToDestroy) {
+    if value.0 % 2 == 0 {
+        to_destroy.0.insert(*entity);
+    }
+}
+
+struct Sum(usize);
+
+#[system_for_each(World)]
+pub fn sum_values(value: &Value, sum: &mut Sum) {
+    sum.0 += value.0;
+}
+
+#[test]
+fn can_destroy_specific() {
+    let mut world = World::default();
+    let _ = world.create(ValueEntity { value: Value(0) });
+    let _ = world.create(ValueEntity { value: Value(1) });
+    let _ = world.create(ValueEntity { value: Value(2) });
+    let _ = world.create(ValueEntity { value: Value(3) });
+    let _ = world.create(ValueEntity { value: Value(4) });
+    let mut to_destroy = ToDestroy(HashSet::new());
+    world.destroy_even_values(&mut to_destroy);
+
+    to_destroy.0.iter().for_each(|entity| {
+        world.destroy(*entity);
+    });
+
+    // 1+3 is 4
+    let mut sum = Sum(0);
+    world.sum_values(&mut sum);
+
+    assert_eq!(4, sum.0);
+}