Type independent traits

Any ways to make the example code work? Would be nice to be able to implement custom traits for abstract classes

trait Container:
    fn __contains__(self, item: AnyType) -> Bool:
        ...


@value
struct List(Container):
    var data: VariadicList[Int]

    fn __contains__(self, item: Int) -> Bool:
        for i in self.data:
            if i == item:
                return True
        return False

trait Container:
    fn __contains__(self, item: AnyType) -> Bool:
        ...


@value
struct List(Container):
    var data: VariadicList[Int]

    fn __contains__(self, item: Int) -> Bool:
        for i in self.data:
            if i == item:
                return True
        return False

9 Replies

benny•6mo ago

I also tried

fn __contains__[*Ts: AnyType](self, item: Ts[0]) -> Bool:
        ...

fn __contains__[*Ts: AnyType](self, item: Ts[0]) -> Bool:
        ...

Hammad Ali•6mo ago

The code throws this error:

struct 'List' does not implement all requirements for 'Container'mojo
main.mojo(2, 5): no '__contains__' candidates have type 'fn(self = List, item = AnyType) -> Bool'
main.mojo(10, 5): candidate declared here with type 'fn(self = List, item = Int) -> Bool'
main.mojo(1, 1): trait 'Container' declared here

struct 'List' does not implement all requirements for 'Container'mojo
main.mojo(2, 5): no '__contains__' candidates have type 'fn(self = List, item = AnyType) -> Bool'
main.mojo(10, 5): candidate declared here with type 'fn(self = List, item = Int) -> Bool'
main.mojo(1, 1): trait 'Container' declared here

I don't think it's possible

Nick!•6mo ago

@benny I think what you want is a generic trait, i.e. the following:

trait Container[T: AnyType]:
    fn __contains__(self, item: T) -> Bool:
        ...
struct List(Container[Int]):

trait Container[T: AnyType]:
    fn __contains__(self, item: T) -> Bool:
        ...
struct List(Container[Int]):

Mojo doesn't support this yet, but it's in the works.

benny•6mo ago

sort of, but i was thinking generic on a function level, where each function can type in different parameters, rather than generic on a struct level

Nick!•6mo ago

I’m not sure what distinction you’re making. Your struct can inherit from that trait multiple times with a different parameter, if you want to have multiple __contains__ functions. There’s also a notion of “associated types” (see Rust and Swift) which avoids the need for the trait to be parametrised.

sora•6mo ago

Sometimes you need both to make a nice api, and good example would be some HasAdd trait, where LHS is generic, and Output is an associated type. IMO, this is why inherit is bad terminology for traits. Could you show some code as your intended usage pattern?

benny•6mo ago

trait Container:
    fn __contains__(self, item: AnyType) -> Bool:
        ...


@value
struct StaticIntList(Container):
    var data: VariadicList[Int]

    fn __contains__(self, item: Int) -> Bool:
        for i in self.data:
            if i == item:
                return True
        return False

@value
struct StaticStringHashTable(Container):
    var data: VariadicList[Int]
    … other attributes and methods for dict

    fn __contains__(self, item: String) -> Bool:
        for i in self.data:
            if i == item:
                return True
        return False

trait Container:
    fn __contains__(self, item: AnyType) -> Bool:
        ...


@value
struct StaticIntList(Container):
    var data: VariadicList[Int]

    fn __contains__(self, item: Int) -> Bool:
        for i in self.data:
            if i == item:
                return True
        return False

@value
struct StaticStringHashTable(Container):
    var data: VariadicList[Int]
    … other attributes and methods for dict

    fn __contains__(self, item: String) -> Bool:
        for i in self.data:
            if i == item:
                return True
        return False

sora•6mo ago

Ah, then you most definitely want associated type, and kinda have to wait.

a2svior•6mo ago

This worked in the previous Mojo version with parameter input, but stopped working in the new version, so I had to remove it for Lightbug 🥲

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Type independent traits