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.