vim regular expression substitution quantifier

Question

how do i quantify the replacement portion of a vim search/replace expression?

:%s/x\{4\}/yyyy/g 

will replace every occurrence of 4 x's with 4 y's.

:%s/x\{4\}/y\{4\}/g 

replaces the 4 x's with "y{4}"

how do i modify that so that i do not have to insert 4 separate y's but instead "quantify" a single y.

Answer 1

The solution seems more troublesome than its worth:

:%s/w\{4}/\=repeat('y',4)/g