Fix E0594: Attempted to Set a Constant with a Non-Constant Value

Fri, 10 Jul 2026 00:44:04 +0800

1. Symptoms

The Rust compiler produces error E0594 when a program attempts to assign a value to a constant that cannot be evaluated at compile time. The compiler emits a clear diagnostic message that identifies the offending assignment and explains the fundamental restriction.

Shell output from cargo build:

error[E0594]: cannot assign to an immutable constant
  --> src/main.rs:6:5
   |
6  |     X = 5;
   |     ^ cannot assign to an immutable constant

error: aborting due to 1 previous error

When the constant in question is initialized with a non-constant expression, the error message provides additional context about the nature of the expression that prevents compile-time evaluation:

E0594 on ErrorVault — Developer Error Code Dictionary

Fix E0594: Attempted to Set a Constant with a Non-Constant Value

1. Symptoms