However:<p>- Almost nobody actually <i>used</i> C prior to 1978.<p>- Most C compilers have supported both current and previous versions of the C standard via <i>-std</i> flags.<p>- Other languages with breaking changes, like Java, are similar. Java has always supported specifying the source language level via <i>-src</i>.<p>Swift is unique in breaking old code completely, without recourse other than semi-functional code rewriting tools.