[phoehne]

Yes, we re-invent the wheel. The more time you spend writing software for a living, the more you will see the wheel re-invented. But Ada and Rust are safe under different definitions of safety. I view Rust as having a more narrow definition of safety, but a very important notion of safety, and executed with brutal focus. While Ada's definition of safety being broader, but better suited to a small subset of use cases.

I write Rust at work. I learned Ada in the early 1990s as the language of software engineering. Back then a lot of the argument against Ada was it was too big, complex, and slowed down development too much. (Not to mention the validating Ada 83 compiler I used cost about $20,000 a seat in today's money). I think the world finally caught up with Ada and we're recognizing that we need languages every bit as big and complex, like Rust, to handle issues like safe, concurrent programming.

[afdbcreid]

I don't know Ada; care to explain why its definition of safety is broader than Rust?

I agree Rust's safety is very clearly (and maybe narrowly) defined, but it doesn't mean there isn't focus on general correctness - there is. The need to define safety precisely arises because it's part of the language (`unsafe`).

[yukeabu]

Rust’s built-in notion of safety is intentionally focused on memory + data-race properties at compile time. logic, timing, and determinism are left to libraries and design. Ada (with SPARK & Ravenscar) treats contracts, concurrency discipline, and timing analysis as first-class language/profile concerns hence a broader safety envelope.

You may choose to think from safety guarantee hierarchy perspective like (Bottom = foundation... Top = highest assurance)

Layer 6: FORMAL PROOFS (functional correctness, no RT errors) Ada/SPARK: built-in (GNATprove) Rust: external tools (Kani, Prusti, Verus)

Layer 5: TIMING / REAL-TIME ANALYSIS (WCET, priority bounds) Ada: Ravenscar profile + scheduling analysis Rust: frameworks (RTIC, Embassy)

Layer 4: CONCURRENCY DETERMINISM (predictable schedules) Ada: protected objects + task priorities Rust: data-race freedom; determinism via design

Layer 3: LOGICAL CONTRACTS & INVARIANTS (pre/post, ranges) Ada: Pre/Post aspects, type predicates (built-in) Rust: type states, assertions, external DbC tools

Layer 2: TYPE SAFETY (prevent invalid states) Ada: range subtypes, discriminants Rust: newtypes, enums, const generics

Layer 1: MEMORY SAFETY & DATA-RACE FREEDOM Ada: runtime checks; SPARK proves statically Rust: compile-time via ownership + Send/Sync

[naasking]

As the OP mentioned, restricted number ranges:

    with Ada.Text_IO; use Ada.Text_IO;

    procedure Restricted_Number_Demo is

        -- Define a restricted subtype of Integer
        subtype Small_Positive is Integer range 1 .. 100;

        -- Define a restricted subtype of Float
        subtype Probability is Float range 0.0 .. 1.0;

        -- Variables of these restricted types
        X : Small_Positive := 42;
        P : Probability    := 0.75;

    begin
        Put_Line("X = " & Integer'Image(X));
        Put_Line("P = " & Float'Image(P));

        -- Uncommenting the following line would raise a Constraint_Error at runtime
        -- X := 200;

    end Restricted_Number_Demo;