Comparing 2 viable solutions --- Solution #0 --- Fixed score: 0 0 0 0 0 0 0 0 0 0 0 ... Constraint restrictions: Cat<Hoge, Int> to Animal<Hoge> is [superclass] Cat<Hoge, Int> to Cat<Hoge, Int> is [deep equality] ... --- Solution #1 --- Fixed score: 0 0 0 0 0 0 0 0 0 0 0 ... Constraint restrictions: Cat<Hoge, Int> to Cat<Hoge, Int> is [deep equality] ...comparing solutions 1 and 0 Comparing declarations func ffoo<U>(_: Cat<Hoge, U>) { } and func ffoo(_: Animal<Hoge>) { } comparison result: not better Comparing declarations func ffoo(_: Animal<Hoge>) { } and func ffoo<U>(_: Cat<Hoge, U>) { } comparison result: betterswift -Xfrontend -debug-constraints a.swift Comparing declarations func foo<T>(_: Animal<T>) { } and func foo<T, U>(_: Cat<T, U>) { } comparison result: not better Comparing declarations func foo<T, U>(_: Cat<T, U>) { } and func foo<T>(_: Animal<T>) { } (found solution 0 0 0 0 0 0 0 0 0 0 0) comparison result: better (edited)