Understanding Rust Error E0741

Introduction

Rust Error E0741 occurs when a non-structural-match type is used as the type of a const generic parameter. This article aims to provide an in-depth explanation, discuss the structural-match types, and offer a solution to fix the error.

What is a structural-match type?

In Rust, a structural-match type is a type that derives both PartialEq and Eq traits and implements the ConstParamTy trait. Using a non-structural-match type in const generic parameters results in Rust Error E0741.

Example of Erroneous Code

Consider the following erroneous code example that demonstrates the Rust Error E0741:

#![allow(unused)]
#![feature(adt_const_params)]

fn main() {
  struct A;

  struct B<const X: A>; // error!
}

Solution

To fix Rust Error E0741, ensure the type used in the const generic parameter is a structural-match type. Derive PartialEq, Eq, and ConstParamTy traits for the type, as shown in the following example:

#![allow(unused)]
#![feature(adt_const_params)]

fn main() {
  use std::marker::ConstParamTy;

  #[derive(PartialEq, Eq, ConstParamTy)] // We derive both traits here.
  struct A;

  struct B<const X: A>; // ok!
}

Conclusion