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Defer

Defer is used to execute a statement while exiting the current block.

const expect = @import("std").testing.expect;

test "defer" {
var x: i16 = 5;
{
defer x += 2;
try expect(x == 5);
}
try expect(x == 7);
}

When there are multiple defers in a single block, they are executed in reverse order.

const expect = @import("std").testing.expect;

test "multi defer" {
var x: f32 = 5;
{
defer x += 2;
defer x /= 2;
}
try expect(x == 4.5);
}

Defer is useful to ensure that resources are cleaned up when they are no longer needed. Instead of needing to remember to manually free up the resource, you can add a defer statement right next to the statement that allocates the resource.