https://m.facebook.com/notes/kent-beck/one-bite-at-a-time-partitioning-complexity/1716882961677894/
blog-post-partitioning-development-complexity#mutable-core-immutable-leavesMutable core/immutable leaves. I hate, loathe, and despise aliasing errors. To avoid them I compose the leaves of my object graph from immutable objects referred to by mutable objects towards the center of the graph. blog-post-partitioning-development-complexity#mutable-core-immutable-leaves
Somewhere in talk-railsconf-keynote-justin-searls he talks about immutable leaves, too