error[E0277]: the size for values of type `(dyn Foo + 'static)` cannot be known at compilation time --> $DIR/issue-111932.rs:4:20 | LL | foos.for_each(|foo| { | ^^^ doesn't have a size known at compile-time | = help: the trait `Sized` is not implemented for `(dyn Foo + 'static)` = note: all function arguments must have a statically known size = help: unsized fn params are gated as an unstable feature error[E0277]: the size for values of type `dyn Foo` cannot be known at compilation time --> $DIR/issue-111932.rs:5:26 | LL | println!("{:?}", foo); | ---- ^^^ doesn't have a size known at compile-time | | | required by a bound introduced by this call | = help: the trait `Sized` is not implemented for `dyn Foo` note: required by a bound in `core::fmt::rt::Argument::<'a>::new_debug` --> $SRC_DIR/core/src/fmt/rt.rs:LL:COL = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info) error: aborting due to 2 previous errors For more information about this error, try `rustc --explain E0277`.