Rust: how to assign `iter().map()` or `iter().enumarate()` to same variable

struct A {...whatever...};
const MY_CONST_USIZE:usize = 127;


// somewhere in function

// vec1_of_A:Vec<A> vec2_of_A_refs:Vec<&A> have values from different data sources and have different inside_item types
let my_iterator;
if my_rand_condition() { // my_rand_condition is random and compiles for sake of simplicity
    my_iterator = vec1_of_A.iter().map(|x| (MY_CONST_USIZE, &x)); // Map<Iter<Vec<A>>>
} else {
    my_iterator = vec2_of_A_refs.iter().enumerate(); // Enumerate<Iter<Vec<&A>>>
}

how to make this code compile?

at the end (based on condition) I would like to have iterator able build from both inputs and I don't know how to integrate these Map and Enumerate types into single variable without calling collect() to materialize iterator as Vec

reading material will be welcomed