Modular•6mo ago

Quick Question on Traits

Hi, Introducing myself to the language and I am wondering how I would get the functionality of being able to pass a conforming type to a function. I tried two ways, the first way is the following code. the second way is the commented code. both ways don't seem to work. EDIT: the error probably helps 😄

error: invalid call to 'hello': argument #1 cannot be converted from 'Dog' to 'Talkable'

error: invalid call to 'hello': argument #1 cannot be converted from 'Dog' to 'Talkable'

Any assistance to help me understand if greatly appreciated!

trait Talkable:
    fn hello(self, thing: Talkable) -> String: ...
    fn goodbye(self, thing: Talkable) -> String: ...
    fn get_name(self) -> String: ...

struct Person(Talkable):
    var name: String
    fn __init__(inout self, name: String):
        self.name = name
    fn hello(self, thing: Talkable) -> String:
        return self.name + " says hello to " + thing.get_name()
    fn goodbye(self, thing: Talkable) -> String:
        return self.name + " says goodbye to " + thing.get_name()
    fn get_name(self) -> String:
        return self.name

struct Dog(Talkable):
    var value: __mlir_type
    var name: String
    var nick_name: String
    var age: Int
    fn __init__(inout self, name: String, nick_name: String, age: Int):
        self.name = name
        self.nick_name = nick_name
        self.age = age

    fn hello(self, thing: Talkable) -> String:
        return self.name + " barks at " + thing.get_name()    
    fn goodbye(self, thing: Talkable) -> String:
        return self.name + " barks at " + thing.get_name()
    
    fn get_name(self) -> String:
        return self.name

# I also tried this from documentation
# fn say_hello[T: Talkable](t1: T, t2: T):
#  t1.hello(t2)


fn main():
    var s = Person(name="Jim")
    var d = Dog("spot", "dog", 2)
    d.hello(s)
    # say_hello(s, d)

trait Talkable:
    fn hello(self, thing: Talkable) -> String: ...
    fn goodbye(self, thing: Talkable) -> String: ...
    fn get_name(self) -> String: ...

struct Person(Talkable):
    var name: String
    fn __init__(inout self, name: String):
        self.name = name
    fn hello(self, thing: Talkable) -> String:
        return self.name + " says hello to " + thing.get_name()
    fn goodbye(self, thing: Talkable) -> String:
        return self.name + " says goodbye to " + thing.get_name()
    fn get_name(self) -> String:
        return self.name

struct Dog(Talkable):
    var value: __mlir_type
    var name: String
    var nick_name: String
    var age: Int
    fn __init__(inout self, name: String, nick_name: String, age: Int):
        self.name = name
        self.nick_name = nick_name
        self.age = age

    fn hello(self, thing: Talkable) -> String:
        return self.name + " barks at " + thing.get_name()    
    fn goodbye(self, thing: Talkable) -> String:
        return self.name + " barks at " + thing.get_name()
    
    fn get_name(self) -> String:
        return self.name

# I also tried this from documentation
# fn say_hello[T: Talkable](t1: T, t2: T):
#  t1.hello(t2)


fn main():
    var s = Person(name="Jim")
    var d = Dog("spot", "dog", 2)
    d.hello(s)
    # say_hello(s, d)

2 Replies

sora•6mo ago

You will need to write type for functions like hello as

fn hello[T: Talkable](self, thing: T) -> String:

fn hello[T: Talkable](self, thing: T) -> String:

Slightly simplified example:

trait Talkable:
    # Use type name `S` here to work around a bug
    fn hello[S: Talkable](self, thing: S) -> String: ...
    fn get_name(self) -> String: ...

@value
struct Person(Talkable):
    var name: String

    fn hello[T: Talkable](self, thing: T) -> String:
        return self.name + " says hello to " + thing.get_name()
    fn get_name(self) -> String:
        return self.name

@value
struct Dog(Talkable):
    var name: String
    var age: Int

    fn hello[T: Talkable](self, thing: T) -> String:
        return self.name + " barks at " + thing.get_name()
    fn get_name(self) -> String:
        return self.name

fn main():
    var s = Person("Jim")
    var d = Dog("Spot", 2)
    print(s.hello(d))

trait Talkable:
    # Use type name `S` here to work around a bug
    fn hello[S: Talkable](self, thing: S) -> String: ...
    fn get_name(self) -> String: ...

@value
struct Person(Talkable):
    var name: String

    fn hello[T: Talkable](self, thing: T) -> String:
        return self.name + " says hello to " + thing.get_name()
    fn get_name(self) -> String:
        return self.name

@value
struct Dog(Talkable):
    var name: String
    var age: Int

    fn hello[T: Talkable](self, thing: T) -> String:
        return self.name + " barks at " + thing.get_name()
    fn get_name(self) -> String:
        return self.name

fn main():
    var s = Person("Jim")
    var d = Dog("Spot", 2)
    print(s.hello(d))

fn say_hello[T: Talkable](t1: T, t2: T):
    t1.hello(t2)

fn say_hello[T: Talkable](t1: T, t2: T):
    t1.hello(t2)

This doesn't work because it requires t1 and t2 to have the same type.

bartimusprimed•6mo ago

Thanks so much! Greatly appreciate the help

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Quick Question on Traits