Rust: chunks_exact variant with const generic argument
In the stdlib I'd like an iterator like chunks_exact that yields fixed-sized arrays, using a const usize argument (mostly useful for short arrays).
.chunks_exact_ct::<3>()
.map(|[a, b, c]| a + b + c)
Those arrays could allow better optimizations and also better pattern matching.
This issue has been assigned to @DutchGhost via this comment.
leonardo-m
👍1
All 11 comments
This also applies to the windows method on slices.
varkor
on 11 May 2019
We should actually be able to implement this and test it out unstably now.
varkor
on 1 Jun 2019
❤3
Im willing to give this a shot in the weekend and next week!
DutchGhost
on 27 Mar 2020
❤1
@rustbot assign @DutchGhost
Dylan-DPC
on 27 Mar 2020
😄1
So, a simple PoC fails to compile horribly
https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=770bf3df27b12c5ce77d5b2a91c5b110
Backtrace
Compiling playground v0.0.1 (/playground)
warning: the feature `const_generics` is incomplete and may cause the compiler to crash
--> src/main.rs:1:12
|
1 | #![feature(const_generics)]
| ^^^^^^^^^^^^^^
|
= note: `#[warn(incomplete_features)]` on by default
thread 'rustc' panicked at 'index out of bounds: the len is 0 but the index is 0', src/librustc_mir_build/hair/pattern/_match.rs:2329:13
stack backtrace:
0: backtrace::backtrace::libunwind::trace
at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/libunwind.rs:86
1: backtrace::backtrace::trace_unsynchronized
at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/mod.rs:66
2: std::sys_common::backtrace::_print_fmt
at src/libstd/sys_common/backtrace.rs:78
3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
at src/libstd/sys_common/backtrace.rs:59
4: core::fmt::write
at src/libcore/fmt/mod.rs:1069
5: std::io::Write::write_fmt
at src/libstd/io/mod.rs:1439
6: std::sys_common::backtrace::_print
at src/libstd/sys_common/backtrace.rs:62
7: std::sys_common::backtrace::print
at src/libstd/sys_common/backtrace.rs:49
8: std::panicking::default_hook::{{closure}}
at src/libstd/panicking.rs:198
9: std::panicking::default_hook
at src/libstd/panicking.rs:218
10: rustc_driver::report_ice
11: std::panicking::rust_panic_with_hook
at src/libstd/panicking.rs:515
12: rust_begin_unwind
at src/libstd/panicking.rs:419
13: core::panicking::panic_fmt
at src/libcore/panicking.rs:111
14: core::panicking::panic_bounds_check
at src/libcore/panicking.rs:69
15: rustc_mir_build::hair::pattern::_match::PatStack::specialize_constructor
16: rustc_mir_build::hair::pattern::_match::is_useful_specialized
17: <core::iter::adapters::Map<I,F> as core::iter::traits::iterator::Iterator>::try_fold
18: rustc_mir_build::hair::pattern::_match::is_useful
19: rustc_mir_build::hair::pattern::check_match::check_not_useful
20: rustc_mir_build::hair::pattern::check_match::check_exhaustive
21: rustc_mir_build::hair::pattern::_match::MatchCheckCtxt::create_and_enter
22: <rustc_mir_build::hair::pattern::check_match::MatchVisitor as rustc_hir::intravisit::Visitor>::visit_expr
23: <rustc_mir_build::hair::pattern::check_match::MatchVisitor as rustc_hir::intravisit::Visitor>::visit_expr
24: rustc_hir::intravisit::walk_expr
25: <rustc_mir_build::hair::pattern::check_match::MatchVisitor as rustc_hir::intravisit::Visitor>::visit_expr
26: rustc_hir::intravisit::walk_expr
27: <rustc_mir_build::hair::pattern::check_match::MatchVisitor as rustc_hir::intravisit::Visitor>::visit_expr
28: rustc_hir::intravisit::walk_block
29: <rustc_mir_build::hair::pattern::check_match::MatchVisitor as rustc_hir::intravisit::Visitor>::visit_expr
30: rustc_hir::intravisit::walk_block
31: <rustc_mir_build::hair::pattern::check_match::MatchVisitor as rustc_hir::intravisit::Visitor>::visit_expr
32: rustc_hir::intravisit::walk_expr
33: <rustc_mir_build::hair::pattern::check_match::MatchVisitor as rustc_hir::intravisit::Visitor>::visit_expr
34: rustc_hir::intravisit::walk_expr
35: <rustc_mir_build::hair::pattern::check_match::MatchVisitor as rustc_hir::intravisit::Visitor>::visit_expr
36: rustc_hir::intravisit::walk_block
37: <rustc_mir_build::hair::pattern::check_match::MatchVisitor as rustc_hir::intravisit::Visitor>::visit_expr
38: rustc_hir::intravisit::walk_block
39: <rustc_mir_build::hair::pattern::check_match::MatchVisitor as rustc_hir::intravisit::Visitor>::visit_expr
40: rustc_hir::intravisit::walk_expr
41: <rustc_mir_build::hair::pattern::check_match::MatchVisitor as rustc_hir::intravisit::Visitor>::visit_expr
42: <rustc_mir_build::hair::pattern::check_match::MatchVisitor as rustc_hir::intravisit::Visitor>::visit_expr
43: <rustc_mir_build::hair::pattern::check_match::MatchVisitor as rustc_hir::intravisit::Visitor>::visit_expr
44: rustc_mir_build::hair::pattern::check_match::check_match
45: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::check_match>::compute
46: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
47: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
48: rustc::ty::<impl rustc::ty::context::TyCtxt>::par_body_owners
49: rustc_session::utils::<impl rustc_session::session::Session>::time
50: rustc_interface::passes::analysis
51: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::analysis>::compute
52: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
53: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
54: rustc::ty::context::tls::enter_global
55: rustc_interface::interface::run_compiler_in_existing_thread_pool
56: rustc_ast::attr::with_globals
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
error: internal compiler error: unexpected panic
note: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports
note: rustc 1.44.0-nightly (75208942f 2020-03-27) running on x86_64-unknown-linux-gnu
note: compiler flags: -C codegen-units=1 -C debuginfo=2 --crate-type bin
note: some of the compiler flags provided by cargo are hidden
query stack during panic:
#0 [check_match] processing `main`
#1 [analysis] running analysis passes on this crate
end of query stack
error: internal compiler error: unexpected const parent in type_of_def_id(): Expr(Expr { hir_id: HirId { owner: DefId(0:29 ~ playground[4875]::main[0]), local_id: 36 }, kind: MethodCall(PathSegment { ident: const_chunks_exact#0, hir_id: Some(HirId { owner: DefId(0:29 ~ playground[4875]::main[0]), local_id: 28 }), res: Some(Err), args: Some(GenericArgs { args: [Const(ConstArg { value: AnonConst { hir_id: HirId { owner: DefId(0:29 ~ playground[4875]::main[0]), local_id: 24 }, body: BodyId { hir_id: HirId { owner: DefId(0:29 ~ playground[4875]::main[0]), local_id: 27 } } }, span: src/main.rs:42:65: 42:75 })], bindings: [], parenthesized: false }), infer_args: false }, src/main.rs:42:44: 42:62, [Expr { hir_id: HirId { owner: DefId(0:29 ~ playground[4875]::main[0]), local_id: 35 }, kind: Array([Expr { hir_id: HirId { owner: DefId(0:29 ~ playground[4875]::main[0]), local_id: 29 }, kind: Lit(Spanned { node: Int(1, Unsuffixed), span: src/main.rs:42:23: 42:24 }), attrs: ThinVec(None), span: src/main.rs:42:23: 42:24 }, Expr { hir_id: HirId { owner: DefId(0:29 ~ playground[4875]::main[0]), local_id: 30 }, kind: Lit(Spanned { node: Int(2, Unsuffixed), span: src/main.rs:42:26: 42:27 }), attrs: ThinVec(None), span: src/main.rs:42:26: 42:27 }, Expr { hir_id: HirId { owner: DefId(0:29 ~ playground[4875]::main[0]), local_id: 31 }, kind: Lit(Spanned { node: Int(3, Unsuffixed), span: src/main.rs:42:29: 42:30 }), attrs: ThinVec(None), span: src/main.rs:42:29: 42:30 }, Expr { hir_id: HirId { owner: DefId(0:29 ~ playground[4875]::main[0]), local_id: 32 }, kind: Lit(Spanned { node: Int(4, Unsuffixed), span: src/main.rs:42:32: 42:33 }), attrs: ThinVec(None), span: src/main.rs:42:32: 42:33 }, Expr { hir_id: HirId { owner: DefId(0:29 ~ playground[4875]::main[0]), local_id: 33 }, kind: Lit(Spanned { node: Int(5, Unsuffixed), span: src/main.rs:42:35: 42:36 }), attrs: ThinVec(None), span: src/main.rs:42:35: 42:36 }, Expr { hir_id: HirId { owner: DefId(0:29 ~ playground[4875]::main[0]), local_id: 34 }, kind: Lit(Spanned { node: Int(6, Signed(I32)), span: src/main.rs:42:38: 42:42 }), attrs: ThinVec(None), span: src/main.rs:42:38: 42:42 }]), attrs: ThinVec(None), span: src/main.rs:42:22: 42:43 }]), attrs: ThinVec(None), span: src/main.rs:42:22: 42:78 })
error: internal compiler error: cat_expr Errd
--> src/main.rs:42:65
|
42 | let mut slice = &[1, 2, 3, 4, 5, 6i32].const_chunks_exact::<{ 1usize }>();
| ^^^^^^^^^^
error: internal compiler error: cat_expr Errd
--> src/main.rs:41:11
|
41 | fn main() {
| ___________^
42 | | let mut slice = &[1, 2, 3, 4, 5, 6i32].const_chunks_exact::<{ 1usize }>();
43 | |
44 | | for [a, b, c] in slice {
45 | | dbg!(a, b, c);
46 | | }
47 | | }
| |_^
error: internal compiler error: cat_expr Errd
--> src/main.rs:42:21
|
42 | let mut slice = &[1, 2, 3, 4, 5, 6i32].const_chunks_exact::<{ 1usize }>();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: internal compiler error: cat_expr Errd
--> src/main.rs:42:22
|
42 | let mut slice = &[1, 2, 3, 4, 5, 6i32].const_chunks_exact::<{ 1usize }>();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: internal compiler error: cat_expr Errd
--> src/main.rs:44:22
|
44 | for [a, b, c] in slice {
| ^^^^^
error: internal compiler error: cat_expr Errd
--> src/main.rs:44:9
|
44 | for [a, b, c] in slice {
| ^^^^^^^^^
error: internal compiler error: cat_expr Errd
--> src/main.rs:44:28
|
44 | for [a, b, c] in slice {
| ____________________________^
45 | | dbg!(a, b, c);
46 | | }
| |_____^
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:14
|
45 | dbg!(a, b, c);
| ^
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:17
|
45 | dbg!(a, b, c);
| ^
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:20
|
45 | dbg!(a, b, c);
| ^
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: internal compiler error: cat_expr Errd
--> src/main.rs:45:9
|
45 | dbg!(a, b, c);
| ^^^^^^^^^^^^^^
|
= note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', src/librustc_errors/lib.rs:360:17
stack backtrace:
0: 0x7fe40417c364 - backtrace::backtrace::libunwind::trace::h03a082ceb81836bc
at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/libunwind.rs:86
1: 0x7fe40417c364 - backtrace::backtrace::trace_unsynchronized::h34510e7f129d298e
at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/mod.rs:66
2: 0x7fe40417c364 - std::sys_common::backtrace::_print_fmt::h52cf6e6445d665be
at src/libstd/sys_common/backtrace.rs:78
3: 0x7fe40417c364 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h355ef422c030af04
at src/libstd/sys_common/backtrace.rs:59
4: 0x7fe4041b9e6c - core::fmt::write::had06c030afbcee40
at src/libcore/fmt/mod.rs:1069
5: 0x7fe40416df83 - std::io::Write::write_fmt::haabb031c309046f2
at src/libstd/io/mod.rs:1439
6: 0x7fe404181185 - std::sys_common::backtrace::_print::h42076b4a9e432704
at src/libstd/sys_common/backtrace.rs:62
7: 0x7fe404181185 - std::sys_common::backtrace::print::he07d5fc37862a4ff
at src/libstd/sys_common/backtrace.rs:49
8: 0x7fe404181185 - std::panicking::default_hook::{{closure}}::h28a0f3917540fbd8
at src/libstd/panicking.rs:198
9: 0x7fe404180ec2 - std::panicking::default_hook::h55a07c2c7f473659
at src/libstd/panicking.rs:218
10: 0x7fe4048001b3 - rustc_driver::report_ice::h76afa7ba8a1313b2
11: 0x7fe404181905 - std::panicking::rust_panic_with_hook::h66d10dbf34a95c6d
at src/libstd/panicking.rs:515
12: 0x7fe406ebee7e - std::panicking::begin_panic::he48f319f5cea64fa
13: 0x7fe406ecb572 - <rustc_errors::HandlerInner as core::ops::drop::Drop>::drop::h5d8fed4f185053ea
14: 0x7fe404839926 - core::ptr::drop_in_place::h37980ff445b6389d
15: 0x7fe404848972 - <alloc::rc::Rc<T> as core::ops::drop::Drop>::drop::hb180bf142d35dd8a
16: 0x7fe40487134d - core::ptr::drop_in_place::h59c5c18d9dba6deb
17: 0x7fe40485bece - rustc_interface::interface::run_compiler_in_existing_thread_pool::h0ddf0d1de30b048f
18: 0x7fe404805b6f - rustc_ast::attr::with_globals::hf6f784271402448f
19: 0x7fe4048143fe - std::sys_common::backtrace::__rust_begin_short_backtrace::he9a56442df093426
20: 0x7fe40485dcee - core::ops::function::FnOnce::call_once{{vtable.shim}}::haa5d5c73f22394b4
21: 0x7fe40415e17f - <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once::hf5535eba2986b63c
at /rustc/75208942f6144daac669e8e382029fc33bdce841/src/liballoc/boxed.rs:1017
22: 0x7fe404191333 - <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once::h855059088bd3c19d
at /rustc/75208942f6144daac669e8e382029fc33bdce841/src/liballoc/boxed.rs:1017
23: 0x7fe404191333 - std::sys_common::thread::start_thread::h6881b5efbe0279f5
at src/libstd/sys_common/thread.rs:13
24: 0x7fe404191333 - std::sys::unix::thread::Thread::new::thread_start::habd9ef16008d1651
at src/libstd/sys/unix/thread.rs:80
25: 0x7fe403ef76db - start_thread
26: 0x7fe40381488f - __clone
27: 0x0 - <unknown>
error: internal compiler error: unexpected panic
note: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports
note: rustc 1.44.0-nightly (75208942f 2020-03-27) running on x86_64-unknown-linux-gnu
note: compiler flags: -C codegen-units=1 -C debuginfo=2 --crate-type bin
note: some of the compiler flags provided by cargo are hidden
query stack during panic:
end of query stack
thread panicked while panicking. aborting.
error: could not compile `playground`.
Notice that a freestanding function does work:
#![feature(const_generics)]
fn const_chunks_exact<T, const N: usize>(slice: &[T]) -> ConstChunksExact<'_, T, { N }> {
assert!(N != 0);
let rem = slice.len() % N;
let len = slice.len() - rem;
let (fst, snd) = slice.split_at(len);
ConstChunksExact::<T, { N }> { v: fst, rem: snd }
}
struct ConstChunksExact<'a, T: 'a, const N: usize> {
v: &'a [T],
rem: &'a [T],
}
impl<'a, T: 'a, const N: usize> Iterator for ConstChunksExact<'a, T, { N }> {
type Item = &'a [T; N];
fn next(&mut self) -> Option<Self::Item> {
if self.v.len() < N {
None
} else {
let (fst, snd) = self.v.split_at(N);
self.v = snd;
let ptr = fst.as_ptr() as *const [T; N];
// SAFETY: ok because we just checked that the length fits
unsafe { Some(&*ptr) }
}
}
}
fn main() {
let mut slice = const_chunks_exact::<_, 3>(&[1, 2, 3, 4, 5, 6i32]);
for [a, b, c] in slice {
dbg!(a, b, c);
}
}
The more I go into this, the more obstacles I stumble upon.
Below a list of all ICE's I encountered:
https://github.com/rust-lang/rust/issues/70586
https://github.com/rust-lang/rust/issues/70507
https://github.com/rust-lang/rust/issues/68596
DutchGhost
on 30 Mar 2020
👍2
Keep going on, those bugs/limitations are worth fixing anyway :)
leonardo-m
on 30 Mar 2020
to_array() could be a new function related to take(), it collects the first N items of an iterator into an array of length given as const generic argument (it panics if the iterator isn't long enough).
Usable like this (using iterate() from itertools):
let nine_foos = iterate(first, |p| foo(p)).to_array::<_, 9>();
to_array() could be a new function related to take(), it collects the first N items of an iterator into an array of length given as const generic argument (it panics if the iterator isn't long enough).
Usable like this (using iterate() from itertools):
let nine_foos = iterate(first, |p| foo(p)).to_array::<_, 9>();
I'd rather implement FromIterator for any [T; N], as that gives you the ability to write iterator.collect::<[_, 10]>(). .to_array could then just forward to that :)
EDIT: This is already PR'd: https://github.com/rust-lang/rust/pull/69985
DutchGhost
on 3 Apr 2020
assert!(N != 0);
We need a good built-in static_assert that works with constant generics too :)
leonardo-m
on 4 Apr 2020
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We should actually be able to implement this and test it out unstably now.