Understanding Rust Error E0033
Introduction to Rust Error E0033
Rust Error E0033 occurs when a trait type is improperly dereferenced. In Rust, traits define a common interface for types, but the size of types implementing a trait can vary. As a result, a trait object has no fixed compile-time size, and accesses to trait types must be through pointers. Error E0033 is triggered when an attempt is made to implicitly dereference a pointer to a trait type.
Erroneous Code Example
#![allow(unused)]
fn main() {
trait SomeTrait { fn method_one(&self){} fn method_two(&self){} }
impl<T> SomeTrait for T {}
let trait_obj: &SomeTrait = &"some_value";
// This tries to implicitly dereference to create an unsized local variable.
let &invalid = trait_obj;
// You can call methods without binding to the value being pointed at.
trait_obj.method_one();
trait_obj.method_two();
}
Fixing the Error
To fix Rust Error E0033, avoid dereferencing the pointer to the trait type. Instead, access the trait methods directly through the pointer:
Fixed Code Example
#![allow(unused)]
fn main() {
trait SomeTrait { fn method_one(&self){} fn method_two(&self){} }
impl<T> SomeTrait for T {}
let trait_obj: &SomeTrait = &"some_value";
// Call the methods directly through the pointer, without dereferencing it.
trait_obj.method_one();
trait_obj.method_two();
}
Summary
In conclusion, Rust Error E0033 is caused by attempting to implicitly dereference a pointer to a trait type. The solution is to access the trait methods directly through the pointer without dereferencing it. Understanding how trait objects work and how to properly handle their pointers is crucial to prevent such errors in Rust code.