Error code E0161

A value was moved whose size was not known at compile time.

Erroneous code example:

trait Bar { fn f(self); } impl Bar for i32 { fn f(self) {} } fn main() { let b: Box<dyn Bar> = Box::new(0i32); b.f(); // error: cannot move a value of type dyn Bar: the size of dyn Bar cannot // be statically determined }

In Rust, you can only move a value when its size is known at compile time.

To work around this restriction, consider "hiding" the value behind a reference: either &x or &mut x. Since a reference has a fixed size, this lets you move it around as usual. Example:

trait Bar { fn f(&self); } impl Bar for i32 { fn f(&self) {} } fn main() { let b: Box<dyn Bar> = Box::new(0i32); b.f(); // ok! }