Title: Hands-on Rust: question about get_component (page 295)

(feel free to respond. “You dug you’re own hole… good luck”)

I have something wrong implementing the “adventurer isn’t an Octopus” code. (Pretty sure it’s “wrong” somewhere else in my code, since I checked and rechecked this specific code several times, but I’m trying to sort out what I may have wrong)

In trying to track down what I’ve done wrong I’ve changed some of the code as follows: (mainly to break a few things out and get some visibility with ```println!()`` calls (adding line numbers to match against stack trace). (also, unfortunately, since this is panicking, it’s actually on picking up the first sword, so not exactly the scenario I’m trying to eventually fix)

40 items 41 .iter(ecs) 42 .filter(|(_entity, _item, &item_pos)| item_pos == player_pos) 43 .for_each(|(entity, _item, _item_pos)| { 44 commands.remove_component::<Point>(*entity); 45 commands.add_component(*entity, Carried(player)); 46 if let Ok(e) = ecs.entry_ref(*entity) { 47 println!("Entity:{:#?}", e.archetype()); 48 let is_weapon = e.get_component::<Weapon>().is_ok(); 49 println!("Entity is weapon: {}", is_weapon); 50 <(Entity, &Carried, &Weapon)>::query() 51 .iter(ecs) 52 .filter(|(_, c, _)| { 53 let is_carried_by_player = c.0 == player; 54 println!( 55 "carried by player: {} {}", 56 is_carried_by_player, is_weapon 57 ); 58 is_carried_by_player && is_weapon 59 }) 60 .for_each(|(e, _, _)| { 61 println!("Remove Weapon Entity"); 62 commands.remove(*e) 63 }) 

For which, I get the following console output:

Entity:Archetype { index: ArchetypeIndex( 10, ), entities: [ Entity( 25, ), Entity( 24, ), Entity( 22, ), Entity( 47, ), Entity( 46, ), Entity( 45, ), Entity( 44, ), Entity( 40, ), Entity( 35, ), Entity( 33, ), Entity( 59, ), Entity( 58, ), Entity( 54, ), Entity( 48, ), Entity( 79, ), Entity( 76, ), ], layout: EntityLayout { components: [ ComponentTypeId { type_id: TypeId { t: 9061793563588654225, }, name: "bracket_geometry::point::Point", }, ComponentTypeId { type_id: TypeId { t: 8331237624739738968, }, name: "dungeoncrawl::components::Render", }, ComponentTypeId { type_id: TypeId { t: 18175530127838128523, }, name: "dungeoncrawl::components::Name", }, ComponentTypeId { type_id: TypeId { t: 14425425821466115813, }, name: "dungeoncrawl::components::Item", }, ComponentTypeId { type_id: TypeId { t: 1855713956641428298, }, name: "dungeoncrawl::components::Damage", }, ComponentTypeId { type_id: TypeId { t: 2499425021939920047, }, name: "dungeoncrawl::components::Weapon", }, ], component_constructors: [ 0x0000000100f9f170, 0x0000000100f9fb50, 0x0000000100fa0200, 0x0000000100f9f2e0, 0x0000000100f9fcd0, 0x0000000100f9f260, ], }, subscribers: Subscribers { len: 0, }, } Entity is weapon: false thread '<unnamed>' panicked at 'called `Result::unwrap()` on an `Err` value: AccessDenied', /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/legion-0.3.1/src/internals/query/mod.rs:340:65 stack backtrace: 0: rust_begin_unwind at /rustc/e1884a8e3c3e813aada8254edfa120e85bf5ffca/library/std/src/panicking.rs:495:5 1: core::panicking::panic_fmt at /rustc/e1884a8e3c3e813aada8254edfa120e85bf5ffca/library/core/src/panicking.rs:92:14 2: core::option::expect_none_failed at /rustc/e1884a8e3c3e813aada8254edfa120e85bf5ffca/library/core/src/option.rs:1268:5 3: core::result::Result<T,E>::unwrap at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/result.rs:973:23 4: legion::internals::query::Query<V,F>::iter_chunks_unchecked at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/legion-0.3.1/src/internals/query/mod.rs:340:24 5: legion::internals::query::Query<V,F>::iter_unchecked at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/legion-0.3.1/src/internals/query/mod.rs:484:9 6: legion::internals::query::Query<V,F>::iter at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/legion-0.3.1/src/internals/query/mod.rs:538:18 7: dungeoncrawl::systems::player_input::player_input::{{closure}} at ./src/systems/player_input.rs:50:29 8: core::iter::traits::iterator::Iterator::for_each::call::{{closure}} at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/iter/traits/iterator.rs:675:29 9: core::iter::adapters::filter_fold::{{closure}} at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/iter/adapters/mod.rs:1071:44 10: core::ops::function::impls::<impl core::ops::function::FnMut<A> for &mut F>::call_mut at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/ops/function.rs:269:13 11: core::iter::traits::iterator::Iterator::fold at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/iter/traits/iterator.rs:2023:21 12: <core::iter::adapters::flatten::FlattenCompat<I,U> as core::iter::traits::iterator::Iterator>::fold::flatten::{{closure}} at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/iter/adapters/flatten.rs:332:30 13: core::ops::function::impls::<impl core::ops::function::FnMut<A> for &mut F>::call_mut at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/ops/function.rs:269:13 14: core::iter::adapters::map_fold::{{closure}} at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/iter/adapters/mod.rs:905:21 15: core::iter::traits::iterator::Iterator::fold at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/iter/traits/iterator.rs:2023:21 16: <core::iter::adapters::fuse::Fuse<I> as core::iter::adapters::fuse::FuseImpl<I>>::fold at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/iter/adapters/fuse.rs:315:19 17: <core::iter::adapters::fuse::Fuse<I> as core::iter::traits::iterator::Iterator>::fold at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/iter/adapters/fuse.rs:106:9 18: <core::iter::adapters::Map<I,F> as core::iter::traits::iterator::Iterator>::fold at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/iter/adapters/mod.rs:945:9 19: <core::iter::adapters::chain::Chain<A,B> as core::iter::traits::iterator::Iterator>::fold at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/iter/adapters/chain.rs:123:19 20: <core::iter::adapters::chain::Chain<A,B> as core::iter::traits::iterator::Iterator>::fold at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/iter/adapters/chain.rs:120:19 21: <core::iter::adapters::flatten::FlattenCompat<I,U> as core::iter::traits::iterator::Iterator>::fold at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/iter/adapters/flatten.rs:335:9 22: <core::iter::adapters::flatten::Flatten<I> as core::iter::traits::iterator::Iterator>::fold at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/iter/adapters/flatten.rs:193:9 23: <core::iter::adapters::Filter<I,P> as core::iter::traits::iterator::Iterator>::fold at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/iter/adapters/mod.rs:1135:9 24: core::iter::traits::iterator::Iterator::for_each at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/iter/traits/iterator.rs:678:9 25: dungeoncrawl::systems::player_input::player_input at ./src/systems/player_input.rs:40:17 26: dungeoncrawl::systems::player_input::player_input_system::{{closure}} at ./src/systems/player_input.rs:10:1 27: <F as legion::internals::systems::system::SystemFn<R,Q>>::run at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/legion-0.3.1/src/internals/systems/system.rs:220:9 28: <legion::internals::systems::system::System<R,Q,F> as legion::internals::systems::schedule::Runnable>::run_unsafe at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/legion-0.3.1/src/internals/systems/system.rs:191:9 29: legion::internals::systems::schedule::Executor::run_recursive at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/legion-0.3.1/src/internals/systems/schedule.rs:384:9 30: legion::internals::systems::schedule::Executor::run_systems::{{closure}} at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/legion-0.3.1/src/internals/systems/schedule.rs:353:34 31: <rayon::iter::for_each::ForEachConsumer<F> as rayon::iter::plumbing::Folder<T>>::consume at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-1.5.0/src/iter/for_each.rs:47:9 32: <rayon::iter::filter::FilterFolder<C,P> as rayon::iter::plumbing::Folder<T>>::consume at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-1.5.0/src/iter/filter.rs:123:24 33: rayon::iter::plumbing::Folder::consume_iter at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-1.5.0/src/iter/plumbing/mod.rs:179:20 34: rayon::iter::plumbing::Producer::fold_with at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-1.5.0/src/iter/plumbing/mod.rs:110:9 35: rayon::iter::plumbing::bridge_producer_consumer::helper at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-1.5.0/src/iter/plumbing/mod.rs:438:13 36: rayon::iter::plumbing::bridge_producer_consumer::helper::{{closure}} at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-1.5.0/src/iter/plumbing/mod.rs:418:21 37: rayon_core::join::join_context::call_a::{{closure}} at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.0/src/join/mod.rs:124:17 38: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/std/src/panic.rs:322:9 39: std::panicking::try::do_call at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/std/src/panicking.rs:381:40 40: ___rust_try 41: std::panicking::try at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/std/src/panicking.rs:345:19 42: std::panic::catch_unwind at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/std/src/panic.rs:396:14 43: rayon_core::unwind::halt_unwinding at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.0/src/unwind.rs:17:5 44: rayon_core::join::join_context::{{closure}} at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.0/src/join/mod.rs:141:24 45: rayon_core::registry::in_worker at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.0/src/registry.rs:879:13 46: rayon_core::join::join_context at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.0/src/join/mod.rs:132:5 47: rayon::iter::plumbing::bridge_producer_consumer::helper at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-1.5.0/src/iter/plumbing/mod.rs:416:47 48: rayon::iter::plumbing::bridge_producer_consumer at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-1.5.0/src/iter/plumbing/mod.rs:397:12 49: <rayon::iter::plumbing::bridge::Callback<C> as rayon::iter::plumbing::ProducerCallback<I>>::callback at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-1.5.0/src/iter/plumbing/mod.rs:373:13 50: <rayon::range::Iter<usize> as rayon::iter::IndexedParallelIterator>::with_producer at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-1.5.0/src/range.rs:112:17 51: rayon::iter::plumbing::bridge at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-1.5.0/src/iter/plumbing/mod.rs:357:12 52: <rayon::range::Iter<usize> as rayon::iter::ParallelIterator>::drive_unindexed at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-1.5.0/src/range.rs:88:17 53: <rayon::iter::filter::Filter<I,P> as rayon::iter::ParallelIterator>::drive_unindexed at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-1.5.0/src/iter/filter.rs:46:9 54: rayon::iter::for_each::for_each at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-1.5.0/src/iter/for_each.rs:12:5 55: rayon::iter::ParallelIterator::for_each at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-1.5.0/src/iter/mod.rs:369:9 56: legion::internals::systems::schedule::Executor::run_systems at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/legion-0.3.1/src/internals/systems/schedule.rs:347:17 57: legion::internals::systems::schedule::Schedule::execute::{{closure}}::{{closure}} at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/legion-0.3.1/src/internals/systems/schedule.rs:518:28 58: rayon_core::join::join::call::{{closure}} at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.0/src/join/mod.rs:102:18 59: rayon_core::join::join_context::call_a::{{closure}} at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.0/src/join/mod.rs:124:17 60: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/std/src/panic.rs:322:9 61: std::panicking::try::do_call at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/std/src/panicking.rs:381:40 62: ___rust_try 63: std::panicking::try at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/std/src/panicking.rs:345:19 64: std::panic::catch_unwind at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/std/src/panic.rs:396:14 65: rayon_core::unwind::halt_unwinding at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.0/src/unwind.rs:17:5 66: rayon_core::join::join_context::{{closure}} at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.0/src/join/mod.rs:141:24 67: rayon_core::registry::Registry::in_worker_cold::{{closure}}::{{closure}} at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.0/src/registry.rs:469:21 68: <rayon_core::job::StackJob<L,F,R> as rayon_core::job::Job>::execute::call::{{closure}} at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.0/src/job.rs:113:21 69: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/std/src/panic.rs:322:9 70: std::panicking::try::do_call at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/std/src/panicking.rs:381:40 71: ___rust_try 72: std::panicking::try at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/std/src/panicking.rs:345:19 73: std::panic::catch_unwind at /Users/mike/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/std/src/panic.rs:396:14 74: rayon_core::unwind::halt_unwinding at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.0/src/unwind.rs:17:5 75: <rayon_core::job::StackJob<L,F,R> as rayon_core::job::Job>::execute at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.0/src/job.rs:119:38 76: rayon_core::job::JobRef::execute at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.0/src/job.rs:59:9 77: rayon_core::registry::WorkerThread::execute at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.0/src/registry.rs:753:9 78: rayon_core::registry::WorkerThread::wait_until_cold at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.0/src/registry.rs:730:17 79: rayon_core::registry::WorkerThread::wait_until at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.0/src/registry.rs:704:13 80: rayon_core::registry::main_loop at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.0/src/registry.rs:837:5 81: rayon_core::registry::ThreadBuilder::run at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.0/src/registry.rs:56:18 82: <rayon_core::registry::DefaultSpawn as rayon_core::registry::ThreadSpawn>::spawn::{{closure}} at /Users/mike/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.0/src/registry.rs:101:20 note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace. 

So my questions are

1 - Am I completely misunderstanding what the archetype() function returns? It looks to me, like it says that the entity DOES have a Weapon component. However the e.get_component::<Weapon>().is_ok() call returns false

2 - Why am I getting an access denied panic (beyond the immediate "because you tried to unwrap() an Err (stupid)?
Item 7 on the stack trace points to my code, but it’s the <(Entity, &Carried, &Weapon)>::query() line and I’m not sure what about that could trigger a panic.