What is the easiest way to swap occurrences of two strings in Vim?

I'd do it like this:

:%s/\v(foo|bar)/\={'foo':'bar','bar':'foo'}[submatch(0)]/g

But that's too much typing, so I'd do this:

function! Mirror(dict)
    for [key, value] in items(a:dict)
        let a:dict[value] = key
    endfor
    return a:dict
endfunction

function! S(number)
    return submatch(a:number)
endfunction

:%s/\v(foo|bar)/\=Mirror({'foo':'bar'})[S(0)]/g

But that still requires typing foo and bar twice, so I'd do something like this:

function! SwapWords(dict, ...)
    let words = keys(a:dict) + values(a:dict)
    let words = map(words, 'escape(v:val, "|")')
    if(a:0 == 1)
        let delimiter = a:1
    else
        let delimiter = '/'
    endif
    let pattern = '\v(' . join(words, '|') . ')'
    exe '%s' . delimiter . pattern . delimiter
        \ . '\=' . string(Mirror(a:dict)) . '[S(0)]'
        \ . delimiter . 'g'
endfunction

:call SwapWords({'foo':'bar'})

If one of your words contains a /, you have to pass in a delimiter which you know none of your words contains, .e.g

:call SwapWords({'foo/bar':'foo/baz'}, '@')

This also has the benefit of being able to swap multiple pairs of words at once.

:call SwapWords({'foo':'bar', 'baz':'quux'})

You can do this easily with Tim Pope's Abolish plugin

:%S/{transmit,receive}/{receive,transmit}

Here is how I swap two words skip & limit:

%s/skip/xxxxx/g | %s/limit/skip/g | %s/xxxxx/limit/g

Pretty sure someone could turn it into a shorter command which accepts two arguments.