References and lifetimes are where Rust wins over Ada, although I agree that Ada has many other great type features.
Access types are unable to express ownership transfer without SPARK (and a sufficiently recent release of gnatprove), and without it the rules for accessibility checks are so complex they're being revamped entirely. And access types can only express lifetimes through lexical scope, which combined with the lack of first-class packages (a la OCaml) means library code just can't define access types with reasonable lifetimes.
Also, I appreciate that Rust is memory safe by default and without toying with a dozen pragmas. Ada needs a profile that guarantees that code can't be the source of erroneous execution and constrains bounded errors further.
Access types are unable to express ownership transfer without SPARK (and a sufficiently recent release of gnatprove), and without it the rules for accessibility checks are so complex they're being revamped entirely. And access types can only express lifetimes through lexical scope, which combined with the lack of first-class packages (a la OCaml) means library code just can't define access types with reasonable lifetimes.
Also, I appreciate that Rust is memory safe by default and without toying with a dozen pragmas. Ada needs a profile that guarantees that code can't be the source of erroneous execution and constrains bounded errors further.