Constant E0010_UNCAPTURED_VARIABLE 

pub const E0010_UNCAPTURED_VARIABLE: ErrorCode;

E0010: Outer variables used in closure but not captured

In Compose, closures must explicitly declare any variables they use from the outer scope. These are listed in a * capture group* before the closure, such as |x| () => .... Compose does not allow implicit capture.

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Example

let x = 1;
let y = 2;
let f = () => x + y;

// autogenerated

✅ Fix:

# let x = 1;
# let y = 2;
let f = |x, y| () => x + y;

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Capture modifiers

Captured variables can be annotated to control how the closure accesses them:

• x — capture by copy (or clone-on-write for complex types)
• mut x — capture as a mutable copy
• ref x — capture a shared reference to a box
• ref mut x — capture a mutable reference to a box

📌 Only variables bound to box values may be captured using ref or ref mut. Owned captures cannot refer to boxed values — this prevents shallow copies of references to heap-allocated data.

Example:

let x = box::new(42);
let f = |ref x| () => print(*x);

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This explicit capture model prevents accidental aliasing and ensures closures make their dependencies and access modes clear.