Bash array fails to populate if function is executed as if condition

I have a function which populates a global bash array

#!/bin/bash

# Array to store debugger IDs
ID=()

fill_id()
{
    for i in 1 2 3 4 5
    do
        ID+=( $i )
    done

    echo "fill_ids      - entries in ID: ${#ID[*]}"
}

If function is called directly, array gets populated and entry count is printed as 5

fill_id
echo "main          - entries in ID: ${#ID[*]}"

Output

fill_ids      - entries in ID: 5
main          - entries in ID: 5

But if function is called in if condition then entry count is printing as 0

if (fill_id)
then
    echo "main          - entries in ID: ${#ID[*]}"
fi

Output

fill_ids      - entries in ID: 5
main          - entries in ID: 0

Return value of fill_fd is not affecting anything either.