Ignoring the impact of using pointer elements in range loops

When not being careful, it’s possible to reference the wrong elements with range loops.

Mistake

Here we are referencing the range variable, customer, which will result in all elements of the customers slice being the same value.

func (s *Store) storeCustomers(customers []Customer) {
	for _, customer := range customers {
    // This pointer is to the range variable customer, not the customers slice
		s.m[customer.ID] = &customer
	}
}

Fix

func (s *Store) storeCustomers(customers []Customer) {
	for _, customer := range customers {
    // create a local variable first
    current := customer
		s.m[customer.ID] = &current
	}
}

References