Vim replace two words with one another

Question

How would one replace all instances of 'foo' with 'bar' and 'bar' with 'foo' in vim?

Answer 1

Take a look at this: how to write only one pattern to exchange two strings in two-ways in vim

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

Answer 2

Aside from using a temporary word for the change, you could also use abolish plugin like this:

:%SubVert/{foo,bar}/{bar,foo}/g