Const-Fn on ErrorVault — Developer Error Code Dictionary

Fix E0791: Dereference of Raw Pointer in Const Fn

Tue, 11 Aug 2026 07:56:04 +0800

1. Symptoms

The Rust compiler emits error E0791 when it encounters raw pointer dereference operations within a const fn context. This error manifests during compilation and prevents the program from building successfully.

When triggered, the compiler produces output similar to the following:

error[E0791]: dereference of raw pointer in const fn
 --> src/main.rs:4:5
  |
4 |     const fn read_value(ptr: *const i32) -> i32 {
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ const fn
...
7 |         unsafe { *ptr }
  |                  ^^^^^^ raw pointer dereference
  |
  = note: const ptr arithmetic is not stable yet
  = note: see issue #71313 <https://github.com/rust-lang/rust/issues/71313> for more information

error: aborting due to 1 previous error

The error message specifically identifies the raw pointer dereference operation (*ptr) and clarifies that the offending function is a const fn. The compiler also references an upstream tracking issue in the Rust repository, indicating this is a limitation of the current stable compiler rather than a fundamental language design choice.

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 E0044: Non-Const Item in Const Context

Wed, 05 Aug 2026 10:20:04 +0800

1. Symptoms

When the Rust compiler encounters E0044, you will see an error message similar to the following in your build output:

error[E0044]: non-constant item in a constant item
  --> src/main.rs:5:5
   |
5  |     static STREAM: Stream = Stream::new();
   |              ^^^^^^ non-constant item

Another common manifestation appears when attempting to use non-const functions within constant contexts:

error[E0044]: non-constant item in a constant item
  --> src/lib.rs:12:8
   |
12 | const VALUE: i32 = compute_value();
   |                  ^^^^^^^^^^^^^ non-constant item

The error specifically indicates that the compiler found a non-constant item where a constant expression was required. This happens during the const-evaluation phase of compilation, where Rust attempts to evaluate expressions at compile time rather than runtime. The compiler rejects these constructs because it cannot guarantee that the referenced items will be deterministically computable during compilation, which is essential for constant evaluation.

Fix E0669: Non-const function call in const context

Sun, 02 Aug 2026 12:44:04 +0800

1. Symptoms

When you encounter error E0669, the Rust compiler produces output similar to the following:

error[E0669]: calls in constants are limited to inherent functions, structs, variants, and trait methods
  --> src/main.rs:6:5
   |
6  |     do_something();
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The error message indicates that the function call cannot be evaluated at compile time because the called function lacks the const qualifier. The compiler explicitly states that constant evaluation contexts are restricted to inherent functions, struct constructors, enum variant constructors, and trait methods that have been marked as const.

Fix E0015: Cannot Call Non-Const Fn in Const Context

Thu, 23 Jul 2026 19:56:04 +0800

1. Symptoms

When your Rust code triggers error E0015, the compiler produces output similar to the following:

error[E0015]: cannot call non-const fn `some_function` in a constant
 --> src/main.rs:5:5
  |
5  |     some_function();
  |     ^^^^^^^^^^^^^^^
  |
  = note: non-const functions may only be called at runtime, in constant
    expressions in the right-hand side of `let` statements with no patterns

This error typically manifests when you attempt to use a runtime function inside a const context, whether that context is a const fn, a static variable, or a const variable declaration. The compiler explicitly rejects the operation because constant evaluation in Rust occurs entirely at compile time, and certain operations—including function calls that the compiler cannot evaluate—are not permitted in this phase.

Fix E0075: Generator/Resume Point Cannot Exist in a Const Context

Wed, 22 Jul 2026 17:32:04 +0800

1. Symptoms

When the Rust compiler encounters E0075, you will see an error message similar to the following during compilation:

error[E0075]: generator/resume point cannot exist in a `const` context
 --> src/main.rs:5:5
  |
5 |     let result = gen.resume();
  |     ^^^^^^^^^^^^^^^^^^^^^^^^

The error indicates that a generator or coroutine’s .resume() method is being invoked in a context that the compiler treats as requiring compile-time evaluation. This typically manifests in const functions, const blocks, or during constant promotion scenarios. The compiler flag E0075 specifically targets the attempt to advance a generator’s state at a point where only compile-time computations are permitted.

Fix E0763: Dereferencing a Raw Pointer in a const fn is Unstable

Tue, 16 Jun 2026 10:20:04 +0800

1. Symptoms

When attempting to dereference a raw pointer inside a const fn, the Rust compiler produces error E0763 with the following message:

error[E0763]: dereferencing a raw pointer in a `const fn` is unstable
  |
  = note: this error occurs in the following function:
  --> src/main.rs:6:1
    |
  6  | const fn get_value(ptr: *const i32) -> i32 {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The compiler may also emit additional notes about requiring nightly features:

  |
  = note: see Rust RFC #2582 for more information about this feature.

In some cases, you might see additional context about requiring specific feature flags:

Fix E0080: Evaluation of Constant Value Failed

Wed, 10 Jun 2026 00:44:04 +0800

1. Symptoms

The Rust compiler produces error E0080 when it encounters a constant expression that cannot be evaluated at compile time. This error manifests in several distinct ways that you should recognize.

Primary Error Message:

error[E0080]: evaluation of constant value failed –> src/main.rs:X:Y | X | const VALUE: Type = expression; | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ attempt to compute value that was never initialized


**Common Variants:**

error[E0080]: evaluation of constant value failed –> src/main.rs:X:Y | X | const VALUE: u32 = 10 / 0; | ^ attempt to divide by zero