3 ms·

I miss coding in Ada. I wish Rust would pillage more of its features. Range types especially seem like they would be at home in the Rust ecosystem.

bobbylarrybobby 3y ago
Rust does have ranges? (They have their problems, namely that they're Iterator instead of IntoIterator and all the problems that entails, but they certainly exist.)
- Jtsummers 3y ago
  Rust ranges aren't types. In Ada you can specify a type like: type Temperature is range -100 .. 300; -- in Celsius, operating range for an aircraft or system perhaps You cannot assign anything outside that range to variables of that type, if the value is known at compile time it won't compile otherwise you get a runtime error (unless you disable checks). You cannot assign an arbitrary integer variable's value (that holds a value in that range) into a variable of type Temperature, you have to cast it. T : Temperature := 500; -- won't compile ... T : Temperature; N : Integer := 50; ... T := N; -- won't compile T := T1 + T2; -- two other temperatures; runtime error if sum is outside -100 .. 300 If you want a subtype range you might do something like: type Days is (Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday); -- an enumeration subtype Weekdays is Days range Monday .. Friday; -- ranges are inclusive in Ada Now you can have a variable of type Days and try to put its value into a variable of type Weekdays and you'll get a runtime error if it's Saturday or Sunday. And you can use these for array indices. These are actual arrays, not dictionaries, so you don't get the performance penalty of a map/dictionary (though generic maps are also available): Schedule : array (Weekdays) of ...; -- fill in with some useful type; Weekdays is the index range D : Days; W : Weekdays; ... W := D; -- will compile, may error at runtime D := Saturday; W := D; -- will error at runtime W := Sunday; -- won't compile W := Monday; -- will compile Schedule(W) := ...;
  - pjmlp 3y ago
    As an addendum, this is something that most Pascal derived languages also support, Object Pascal, Mesa, Modula variants, (with exception of Oberon and its linage), and sadly many associate only to Ada.
mbStavola 3y ago
I have good news for you then-- there already is some experimental[0] work towards this, under the name of "pattern types" (although I believe it's on pause at the moment). The idea seems to be to pull some of the pattern semantics into the type system, allowing for more than just range types, based on a series of blog posts[1] by the author of the PR. Additionally, Yoshua Wuyts has another blog post[2] which gives a decent intro on the concept and what it could be used for down the line. [1]: https://github.com/rust-lang/rust/pull/107606 https://github.com/rust-lang/rust/pull/107606 [2]: https://cohost.org/oli-obk/post/165584-ranged-integers-via https://cohost.org/oli-obk/post/165584-ranged-integers-via [3]: https://blog.yoshuawuyts.com/pattern-extensions/#pattern-types https://blog.yoshuawuyts.com/pattern-extensions/#pattern-typ...

bobbylarrybobby 3y ago

Rust does have ranges? (They have their problems, namely that they're Iterator instead of IntoIterator and all the problems that entails, but they certainly exist.)

Jtsummers 3y ago
Rust ranges aren't types. In Ada you can specify a type like: type Temperature is range -100 .. 300; -- in Celsius, operating range for an aircraft or system perhaps You cannot assign anything outside that range to variables of that type, if the value is known at compile time it won't compile otherwise you get a runtime error (unless you disable checks). You cannot assign an arbitrary integer variable's value (that holds a value in that range) into a variable of type Temperature, you have to cast it. T : Temperature := 500; -- won't compile ... T : Temperature; N : Integer := 50; ... T := N; -- won't compile T := T1 + T2; -- two other temperatures; runtime error if sum is outside -100 .. 300 If you want a subtype range you might do something like: type Days is (Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday); -- an enumeration subtype Weekdays is Days range Monday .. Friday; -- ranges are inclusive in Ada Now you can have a variable of type Days and try to put its value into a variable of type Weekdays and you'll get a runtime error if it's Saturday or Sunday. And you can use these for array indices. These are actual arrays, not dictionaries, so you don't get the performance penalty of a map/dictionary (though generic maps are also available): Schedule : array (Weekdays) of ...; -- fill in with some useful type; Weekdays is the index range D : Days; W : Weekdays; ... W := D; -- will compile, may error at runtime D := Saturday; W := D; -- will error at runtime W := Sunday; -- won't compile W := Monday; -- will compile Schedule(W) := ...;
- pjmlp 3y ago
  As an addendum, this is something that most Pascal derived languages also support, Object Pascal, Mesa, Modula variants, (with exception of Oberon and its linage), and sadly many associate only to Ada.

mbStavola 3y ago

I have good news for you then-- there already is some experimental[0] work towards this, under the name of "pattern types" (although I believe it's on pause at the moment). The idea seems to be to pull some of the pattern semantics into the type system, allowing for more than just range types, based on a series of blog posts[1] by the author of the PR. Additionally, Yoshua Wuyts has another blog post[2] which gives a decent intro on the concept and what it could be used for down the line. [1]: https://github.com/rust-lang/rust/pull/107606 https://github.com/rust-lang/rust/pull/107606 [2]: https://cohost.org/oli-obk/post/165584-ranged-integers-via https://cohost.org/oli-obk/post/165584-ranged-integers-via [3]: https://blog.yoshuawuyts.com/pattern-extensions/#pattern-types https://blog.yoshuawuyts.com/pattern-extensions/#pattern-typ...