5 ms·

I mean, int[5] and int[7] would be different types, and lots of bugs happen from passing something besides the appropriate array type to a function. That being

I mean, int[5] and int[7] would be different types, and lots of bugs happen from passing something besides the appropriate array type to a function. That being said, most languages which disambiguate between int[5] and int[7] provide some kind of polymorphism (and usually store it as a struct of size + data, to enable that). For example: you can define a first function that goes from t[N]->t pretty easily, and it would operate on both int[5] and int[7] (returning an int).

pasquinelli 10y ago
Right, in a language with dependent types there is a type-level difference between int[5] and int[7], but c is not such a language, therefore using a syntax that encourages the mistaken notion that there is a type-level difference between int[5] and int[7] would be misleading.
- Vogtinator 10y ago
  There is a small type difference in C, sizeof() of those two types is different.
- Nullabillity 10y ago
  Saying int[5] and int[7] are the same type because the compiler doesn't enforce the difference is like saying JavaScript is untyped because there is no compiler to enforce types at all. Regardless of what the spec or the compiler says, you the programmer absolutely need to treat them separately. Especially in a language like C, where arrays aren't even self-describing at runtime.
  - pasquinelli 10y ago
    no it isn't. javascript has types; they exist only at runtime, but they're there. it's patently false to say it's untyped. but type differences codify certain classes of differences, and it really isn't that crazy or unusual to say that the length of a vector, array, list, whatever you want to call it, isn't a difference of type. to say that there's a type difference even if the type checker disagrees just means you and the type checker are using different type systems.
- kibwen 10y ago
  A language doesn't need dependent types to make fixed-size arrays of differing size count as incompatible types. Rust does this, for example: // error: expected an array with a fixed size of 5 // elements, found one with 7 elements let x: [i32; 5] = [1,2,3,4,5,6,7];
  - pasquinelli 10y ago
    i don't know rust, but i read a bit about fixed size arrays in it and the fact that 32 is the largest fixed size array makes me suspicious that it works like a pair. you can do this without depending on a value, because the length is encoded in the type. like, you can have a type (a, b), and b can, of course, be of type (a, b), b again having type (a, b), and so on. then you always carry around the length encoded in the type, and it can be checked like above. ghc has a limit on tuple sizes, and haskell makes no type distinction between [a] based on the number of elements in it, and it isn't dependently typed. but again i don't know rust.
    - kibwen 10y ago
      > i read a bit about fixed size arrays in it and the fact > that 32 is the largest fixed size array This is exceptionally mistaken, where did you read it? Arrays in Rust top out at the maximum value of a platform-sized pointer, which is either 2^32 or 2^64 depending on platform.
      - pasquinelli 10y ago
        "Arrays of sizes from 0 to 32 (inclusive) implement the following traits if the element type allows it: Clone (only if T: Copy) Debug IntoIterator (implemented for &[T; N] and &mut [T; N]) PartialEq, PartialOrd, Eq, Ord Hash AsRef, AsMut Borrow, BorrowMut Default This limitation on the size N exists because Rust does not yet support code that is generic over the size of an array type. [Foo; 3] and [Bar; 3] are instances of same generic type [T; 3], but [Foo; 3] and [Foo; 5] are entirely different types. As a stopgap, trait implementations are statically generated up to size 32." from the rust docs. https://doc.rust-lang.org/std/primitive.array.html https://doc.rust-lang.org/std/primitive.array.html i sort of leapt to the conclusion that these traits couldn't be implemented because generically because the type system requires them to be implemented for each size of N, and they provide the first 32 as a nicety. the similarity to the situation with tuples in haskell, (http://stackoverflow.com/questions/2978389/haskell-tuple-size-limit http://stackoverflow.com/questions/2978389/haskell-tuple-siz...), and the fact that rust doesn't have dependent types and so a type couldn't depend on a value, and i just kind of guessed at a possible reason.
flukus 10y ago
Are there languages where these would be different types? Could they still be passed to a function that accepts a variable length array?

pasquinelli 10y ago

Right, in a language with dependent types there is a type-level difference between int[5] and int[7], but c is not such a language, therefore using a syntax that encourages the mistaken notion that there is a type-level difference between int[5] and int[7] would be misleading.

Vogtinator 10y ago
There is a small type difference in C, sizeof() of those two types is different.
Nullabillity 10y ago
Saying int[5] and int[7] are the same type because the compiler doesn't enforce the difference is like saying JavaScript is untyped because there is no compiler to enforce types at all. Regardless of what the spec or the compiler says, you the programmer absolutely need to treat them separately. Especially in a language like C, where arrays aren't even self-describing at runtime.
- pasquinelli 10y ago
  no it isn't. javascript has types; they exist only at runtime, but they're there. it's patently false to say it's untyped. but type differences codify certain classes of differences, and it really isn't that crazy or unusual to say that the length of a vector, array, list, whatever you want to call it, isn't a difference of type. to say that there's a type difference even if the type checker disagrees just means you and the type checker are using different type systems.
kibwen 10y ago
A language doesn't need dependent types to make fixed-size arrays of differing size count as incompatible types. Rust does this, for example: // error: expected an array with a fixed size of 5 // elements, found one with 7 elements let x: [i32; 5] = [1,2,3,4,5,6,7];
- pasquinelli 10y ago
  i don't know rust, but i read a bit about fixed size arrays in it and the fact that 32 is the largest fixed size array makes me suspicious that it works like a pair. you can do this without depending on a value, because the length is encoded in the type. like, you can have a type (a, b), and b can, of course, be of type (a, b), b again having type (a, b), and so on. then you always carry around the length encoded in the type, and it can be checked like above. ghc has a limit on tuple sizes, and haskell makes no type distinction between [a] based on the number of elements in it, and it isn't dependently typed. but again i don't know rust.
  - kibwen 10y ago
    > i read a bit about fixed size arrays in it and the fact > that 32 is the largest fixed size array This is exceptionally mistaken, where did you read it? Arrays in Rust top out at the maximum value of a platform-sized pointer, which is either 2^32 or 2^64 depending on platform.
    - pasquinelli 10y ago
      "Arrays of sizes from 0 to 32 (inclusive) implement the following traits if the element type allows it: Clone (only if T: Copy) Debug IntoIterator (implemented for &[T; N] and &mut [T; N]) PartialEq, PartialOrd, Eq, Ord Hash AsRef, AsMut Borrow, BorrowMut Default This limitation on the size N exists because Rust does not yet support code that is generic over the size of an array type. [Foo; 3] and [Bar; 3] are instances of same generic type [T; 3], but [Foo; 3] and [Foo; 5] are entirely different types. As a stopgap, trait implementations are statically generated up to size 32." from the rust docs. https://doc.rust-lang.org/std/primitive.array.html https://doc.rust-lang.org/std/primitive.array.html i sort of leapt to the conclusion that these traits couldn't be implemented because generically because the type system requires them to be implemented for each size of N, and they provide the first 32 as a nicety. the similarity to the situation with tuples in haskell, (http://stackoverflow.com/questions/2978389/haskell-tuple-size-limit http://stackoverflow.com/questions/2978389/haskell-tuple-siz...), and the fact that rust doesn't have dependent types and so a type couldn't depend on a value, and i just kind of guessed at a possible reason.

flukus 10y ago

Are there languages where these would be different types? Could they still be passed to a function that accepts a variable length array?