rust - Is it possible to store a value in a struct through a trait? -

editor's note: code example version of rust prior 1.0 , not syntactically valid rust 1.0 code. updated versions of code produce different errors, answers still contain valuable information.

i tried , without box, , without lifetimes:

trait traittoimpl {     fn do_something(self, val: i32); }  struct cont {     value: i32, }  impl traittoimpl cont {     fn do_something(self, val: i32) {         println!("{}", val);     } }  struct storetrait<'a> {     field: box<traittoimpl + 'a>, }  fn main() {     let cont = box::new(cont { value: 12 }) box<traittoimpl>;     let = storetrait { field: cont };     a.field.do_something(123); } 

all error:

error: cannot convert trait object because trait `traittoimpl` not object-safe

the problem is, error message says, trait traittoimpl not object safe. is, not safe use particular trait through reference (i.e. &traittoimpl or box<traittoimpl>.

specifically, do_something method takes self value. consider: how compiler call method on cont that's been placed in box<traittoimpl>? has copy value argument of type cont (which impl expects), call has work any type of any size might implement traittoimpl!

practical upshot: if have trait contains by-value self, or generics, cannot used via reference. @ point call happens, compiler no longer has enough information generate necessary code.

maybe try taking &self instead? :)