error[E0277]: expected a `std::ops::Fn<(_,)>` closure, found `impl std::ops::Fn<(((_, _), _),)>` --> src/main.rs:32:12 | 32 | let t8 = pair_panic(t7, o_panic(f, g)); | ^^^^^^^^^^ expected an `Fn<(_,)>` closure, found `impl std::ops::Fn<(((_, _), _),)>` | = help: the trait `std::ops::Fn<(_,)>` is not implemented for `impl std::ops::Fn<(((_, _), _),)>` note: required by `pair_panic` --> src/main.rs:9:1 | 9 | / fn pair_panic<A,B,C>( f:impl Fn(A) -> B, g:impl Fn(A) -> C ) -> impl Fn(A) -> (B,C) 10 | | where 11 | | A: Copy 12 | | { ... | 18 | | } 19 | | } | |_^ error: aborting due to previous error For more information about this error, try `rustc --explain E0277`. error: Could not compile `panic`. To learn more, run the command again with --verbose. 

thread 'rustc' panicked at 'assertion failed: result', src/librustc/traits/select.rs:2779:13 note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace. stack backtrace: 0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace 1: std::sys_common::backtrace::_print 2: std::panicking::default_hook::{{closure}} 3: std::panicking::default_hook 4: rustc::util::common::panic_hook 5: std::panicking::rust_panic_with_hook 6: std::panicking::begin_panic 7: rustc::infer::InferCtxt::in_snapshot 8: rustc::traits::select::SelectionContext::confirm_candidate 9: rustc::traits::select::SelectionContext::select 10: rustc_data_structures::obligation_forest::ObligationForest<O>::process_obligations 11: <rustc::traits::fulfill::FulfillmentContext as rustc::traits::engine::TraitEngine>::select_where_possible 12: rustc_typeck::check::FnCtxt::select_obligations_where_possible 13: rustc_typeck::check::FnCtxt::check_argument_types 14: rustc_typeck::check::callee::<impl rustc_typeck::check::FnCtxt>::confirm_builtin_call 15: rustc_typeck::check::callee::<impl rustc_typeck::check::FnCtxt>::check_call 16: rustc_typeck::check::FnCtxt::check_expr_kind 17: rustc_typeck::check::FnCtxt::check_expr_with_expectation_and_needs 18: rustc_typeck::check::FnCtxt::check_decl_initializer 19: rustc_typeck::check::FnCtxt::check_decl_local 20: rustc_typeck::check::FnCtxt::check_stmt 21: rustc_typeck::check::FnCtxt::check_block_with_expected 22: rustc_typeck::check::FnCtxt::check_expr_kind 23: rustc_typeck::check::FnCtxt::check_expr_with_expectation_and_needs 24: rustc_typeck::check::FnCtxt::check_return_expr 25: rustc_typeck::check::check_fn 26: rustc::ty::context::GlobalCtxt::enter_local 27: rustc_typeck::check::typeck_tables_of 28: rustc::ty::query::__query_compute::typeck_tables_of 29: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::typeck_tables_of>::compute 30: rustc::dep_graph::graph::DepGraph::with_task_impl 31: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query 32: rustc::ty::<impl rustc::ty::context::TyCtxt>::par_body_owners 33: rustc_typeck::check::typeck_item_bodies 34: rustc::ty::query::__query_compute::typeck_item_bodies 35: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::typeck_item_bodies>::compute 36: rustc::dep_graph::graph::DepGraph::with_task_impl 37: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query 38: rustc::util::common::time 39: rustc_typeck::check_crate 40: rustc_interface::passes::analysis 41: rustc::ty::query::__query_compute::analysis 42: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::analysis>::compute 43: rustc::dep_graph::graph::DepGraph::with_task_impl 44: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query 45: rustc::ty::context::tls::enter_global 46: rustc_interface::passes::BoxedGlobalCtxt::access::{{closure}} 47: rustc_interface::passes::create_global_ctxt::{{closure}} 48: rustc_interface::passes::BoxedGlobalCtxt::enter 49: rustc_interface::interface::run_compiler_in_existing_thread_pool 50: std::thread::local::LocalKey<T>::with 51: scoped_tls::ScopedKey<T>::set 52: syntax::with_globals query stack during panic: #0 [typeck_tables_of] processing `main` #1 [typeck_item_bodies] type-checking all item bodies #2 [analysis] running analysis passes on this crate end of query stack 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 1.35.0-nightly (fbd34efb3 2019-03-26) running on x86_64-apple-darwin note: compiler flags: -C debuginfo=2 -C incremental --crate-type bin note: some of the compiler flags provided by cargo are hidden error: Could not compile `rust`. To learn more, run the command again with --verbose.