Scope, use, and watch

Overview

Echo has a strict function scope model. Outer variables are not automatically visible inside functions.

Syntax

use name;
use mut count;
watch count;

Example

count: int = 0;
watch count;

fn bump() {
    use mut count;
    count = count + 1;
}

bump();

Output

WATCH: count changed to 1 (in global)

Notes

use

Imports an outer variable for reading inside a function.

use mut

Imports an outer variable for mutation inside a function.

watch

Marks a variable for change reporting.

Shadowing

Declaring a local typed variable with the same name as a parent variable can trigger a warning.

Common Mistakes

• Reading outer variables without use
• Mutating outer variables without use mut
• Watching an undefined variable

Current Limitation

Echo's function scope is stricter than typical lexical closures. That is intentional in the current implementation.

See Also

• Functions
• Errors and Troubleshooting