It's impossible for Rust to have sane HKT

2 days ago

Rust reifies regions as types, using subtyping and variance for lifetime checks.
Lifetime parameters in data structures complicate type abstraction and variance.
Abstracting over generic types (HKT) is desired but problematic in Rust due to lifetime reification.
Lifetimes as first-class types mix technical propositions with business logic, causing abstraction issues.
Attempts to work around lifetime parameters in traits lead to complex and ugly solutions.
Higher-kinded types (HKT) in Rust are fundamentally hindered by lifetime reification.
Variadic kinds could theoretically solve the problem but would make Rust's type system undecidable and complex.
Generic Associated Types (GATs) do not fully solve the abstraction-over-lifetimes problem.
Rust's design has a deep category error by conflating lifetimes with business logic types.
Scala 3's Capture Checking is cited as a better approach to reification.

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