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

Question

What is the easiest way to replace all occurrences of string_a with string_b while at the same time changing anything that was already string_b into string_a? My current method is as follows:

:s/string_a/string_c/g  
:s/string_b/string_a/g  
:s/string_c/string_b/g  

Although this works, it requires extra typing and seems inefficient. Does anybody know of a better way to do this?

Answer 1

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'})