Whilst it may appear that concatenation of strings is easier in other (more declarative) languages, in practice, understanding the runtime performance/complexit

Whilst it may appear that concatenation of strings is easier in other (more declarative) languages, in practice, understanding the runtime performance/complexity and memory usage/lifetimes is far from trivial. Sure, a more declarative language might still be preferable, but for those who need better control and more ability to reason about how the program with execute, the Rust approach makes sense.