enums - How to extend the lifetimes of Strings within functions of traits that require returning &str? -

problem

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i trying implement std::error::error trait on enum. elements of enum enum variants, , generate different error message containing data variant. implementation below formatted string deref &str don't live long enough.

the general solution return string. however, not option here returned type must &str specified error trait.

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example: playground link

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it important note variants may not contain usize, , might instead enum, or struct etc.

use std::fmt; use std::fmt::{display, formatter}; use std::error;  #[derive(debug)] enum enumerror {     a,     b(usize),     c(usize),     d, }  impl error::error enumerror {     fn description(&self) -> &str {         use enumerror::*;         match *self {             => "a happened",             b(value) => &*format!("b happened info: {:?}", value),             c(value) => &*format!("b happened info: {:?}", value),             d => "d happened",         }     } }  impl display enumerror {     fn fmt(&self, f: &mut formatter) -> fmt::result {     use std::error::error;         write!(f, "{}", self.description())     } }  fn main() {} 

the string create needs owned something. when create local string in method, have transfer ownership caller. since have return &str, not option.

the way around store string in struct itself. can declare enum value b(usize, string), put description there when create it, , return with

b(_, ref descr) => descr 

to frank, description not supposed terribly detailed message, needs give general description of kind of error is, why returns &str. didn't see instances of writing dynamic data description in standard library, it's static string. display implementation different matter though, in there can more verbose.