A variable used inside an inner function comes from a dynamic environment.
Erroneous code example:
fn foo() {
let y = 5;
fn bar() -> u32 {
y // error: can't capture dynamic environment in a fn item; use the
// || { ... } closure form instead.
}
}Inner functions do not have access to their containing environment. To fix this error, you can replace the function with a closure:
fn foo() {
let y = 5;
let bar = || {
y
};
}Or replace the captured variable with a constant or a static item:
fn foo() {
static mut X: u32 = 4;
const Y: u32 = 5;
fn bar() -> u32 {
unsafe {
X = 3;
}
Y
}
}