But then you would need a local dt for each time-dependent function, and shaders don't really have packaged-up member variables in structs like you think they w

But then you would need a local dt for each time-dependent function, and shaders don't really have packaged-up member variables in structs like you think they would if you come from Rust. That means you would have to maintain a massive list of dt's for each time-dependent function your shader calls, and then change this list everytime you introduce or remove a time-dependent function to the shader code. It's a solution that only works in a language that can hide the complexity from the programmer like Rust.