Fix E0493: Destructor Cannot Be Called in Constant Function

Sat, 08 Aug 2026 22:20:04 +0800

1. Symptoms

When the Rust compiler encounters E0493, it produces an error message indicating that a destructor cannot be invoked during constant evaluation. The compiler provides context about which type’s destructor is problematic and where the invalid call occurs.

Typical compiler output looks like this:

error[E0493]: destructor of `MyStruct` cannot be called in constant function
  --> src/main.rs:10:5
   |
10 |     drop(value);
   |     ^^^^^^^^^^^ calling the destructor of `MyStruct` in constant function

The error manifests in several common scenarios. When using the drop function on a type that implements Drop inside a const fn, the compiler rejects the code. Similarly, when a constant initialization implicitly requires destructor execution, such as when a const value goes out of scope during const evaluation, the same error appears. Explicit calls to std::mem::drop within constant contexts also trigger this error when the dropped type has a custom destructor.

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:

Compile-Time Evaluation on ErrorVault — Developer Error Code Dictionary

Fix E0493: Destructor Cannot Be Called in Constant Function

1. Symptoms

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

1. Symptoms