Implicit Conversions vs. Extension Methods: Which yields better type safety for DSL design?

Designing a Domain‑Specific Language

When building a DSL in Scala, developers often choose between implicit conversions and Scala 3 extension methods to expose expressive syntax. The goal is to maintain type safety while keeping the API readable and future‑proof.

Implicit conversions allow concise syntax but rely on the implicit resolution mechanism, which can introduce hidden dependencies, ambiguous overloads, and obscure compile‑time errors. Extension methods, introduced in Scala 3, provide explicit, type‑safe syntax and better tooling support, yet they require a Scala 3 codebase and may not interoperate with existing Scala 2 libraries that depend on implicits.

Given this trade‑off, which approach offers stronger guarantees against accidental ambiguity and runtime failures when designing a sealed‑trait DSL, and how does each affect long‑term compatibility with Scala 2 ecosystems?

1. Does using extension methods reduce the risk of ambiguous implicit resolution compared to implicit conversions for DSL design?

2. What impact does each approach have on compile‑time diagnostics and tooling support?

3. How does the choice affect future compatibility with Scala 2 libraries that rely on implicit conversions?