Using Rust as an example, both the borrow checker ("region-based memory management": https://www.cs.umd.edu/projects/cyclone/papers/cyclone-regions.pdf https://

Using Rust as an example, both the borrow checker ("region-based memory management": https://www.cs.umd.edu/projects/cyclone/papers/cyclone-regions.pdf https://www.cs.umd.edu/projects/cyclone/papers/cyclone-regio... ) and affine types were "useless" in that they failed to find any practical adoption in industry... until they suddenly weren't. Nearly the entire field of mathematics is "useless" in this way, until one day somebody accidentally invents Boolean algebra or Fourier transforms or etc. and changes the world in the process.