Generate permutations with symbols

Goal: Create a combination of emails based from inputted first name, last name, middle name, and a domain. Add in common separators. Then I'll check which one is correct with the rapportive API. This is the first part of the bigger script.

If you are given the string variables

{fn}
{ln}
{fi}
{li}
{mi}
{mn}

How would you create the following?

{fn}
{ln}
{fn}{ln}
{fn}.{ln}
{fi}{ln}
{fi}.{ln}
{fn}{li}
{fn}.{li}
{fi}{li}
{fi}.{li}
{ln}{fn}
{ln}.{fn}
{ln}{fi}
{ln}.{fi}
{li}{fn}
{li}.{fn}
{li}{fi}
{li}.{fi}
{fi}{mi}{ln}
{fi}{mi}.{ln}
{fn}{mi}{ln}
{fn}.{mi}.{ln}
{fn}{mn}{ln}
{fn}.{mn}.{ln}
{fn}-{ln}
{fi}-{ln}
{fn}-{li}
{fi}-{li}
{ln}-{fn}
{ln}-{fi}
{li}-{fn}
{li}-{fi}
{fi}{mi}-{ln}
{fn}-{mi}-{ln}
{fn}-{mn}-{ln}
{fn}_{ln}
{fi}_{ln}
{fn}_{li}
{fi}_{li}
{ln}_{fn}
{ln}_{fi}
{li}_{fn}
{li}_{fi}
{fi}{mi}_{ln}
{fn}_{mi}_{ln}
{fn}_{mn}_{ln}

at the moment I am solving it by creating an array for each permutation

```
fi_perms = [fi].product ['_' + li,
'_' + ln,
'-' +li,
'-' ln,
'.' + li,
'.' + ln,
li,
ln,

Since your list is not "all permutation", but is painstakingly built by hand, I would not suggest using array's permutation API or something like that, but keep the curated mode you are using.

I would suggest building it in a more readable way. In your way of [fi].product[...] it is very hard to follow which permutation exists, and which doesn't. The first list you show is more readable, and if you name your atoms correctly (first_name instead of fn), it makes it trivial to understand what you are trying to do. I would suggest building your permutation table as a string like this:

name_permutations = <<PERMS
{last_initial}{first_name}
{last_initial}.{first_name}
{last_initial}{first_initial}
{last_initial}.{first_initial}
{first_initial}{middle_initial}{last_name}
{first_initial}{middle_initial}.{last_name}
{first_name}{middle_initial}{last_name}
{first_name}.{middle_initial}.{last_name}
{first_name}{middle_name}{last_name}
{first_name}.{middle_name}.{last_name}
{first_name}-{last_name}
{first_initial}-{last_name}
{first_name}-{last_initial}
{first_initial}-{last_initial}
{last_name}-{first_name}
{last_name}-{first_initial}
{last_initial}-{first_name}
{last_initial}-{first_initial}
...
PERMS

And then use substitutions to get all permutations:

name_permutations.gsub('{first_name}', first_name)
                 .gsub('{last_name}', last_name)
                 .gsub('{middle_name}', middle_name)
                 .gsub('{first_initial}', first_initial)
                 .gsub('{middle_initial}', middle_initial)
                 .gsub('{last_initial}', last_initial)
                 .split($/)

StackExchange Code Review Q#43373, answer score: 3