Worth noting that even though Rust doesn't let you have two separate pieces of code share responsibility for actually initializing a data structure, in practice

Worth noting that even though Rust doesn't let you have two separate pieces of code share responsibility for actually initializing a data structure, in practice that doesn't lead to much, if any, code duplication: a Foo::new() can usually be written as a wrapper around a call to Foo::new_with_options(x, y, z).