The code below fails.
fn greet(n: Bool) -> String:
return "Hello, 2!"
fn greet(name: String) -> String:
return "Hello, " + name + "!"
fn main():
print(greet("hi"))
print(greet(False))
Add a comment
|
1 Answer
First, welcome to Mojo🔥!
You are really close. I see two issues:
- Your
Boolversion ofgreet()is not using the arg, which will cause the compiler to be fussy. Therefore, in the example below, I added an evaluation ofnjust to quickly skip past this issue. - Calling
greet("hi")is passing aStringLiteraland not aString. By usingstr()around the"hi"you get that converted to aString.
# file __temp/overload.mojo
fn greet(n: Bool) -> String:
if n:
return "Hello! 'n' was True!"
else:
return "Heya! 'n' was False!"
fn greet(name: String) -> String:
return "Hello, " + name + "!"
fn main():
print(greet(str("world")))
print(greet(False))
Result:
Hello, world!
Heya! 'n' was False!
Also, instead of worrying about String vs StringLiteral, you could use the Stringable trait. That identifies any object (including your own custom concoctions) that provide a __str__() -> String method.
# updated file contents
fn greet(n: Bool) -> String:
if n:
return "Hello! 'n' was True!"
else:
return "Heya! 'n' was False!"
fn greet[T: Stringable](name: T) -> String:
return "Hello, " + str(name) + "!"
@value
struct MyStruct(Stringable):
var some_data: Int
var more_data: Bool
fn __str__(self) -> String:
return "Call me Bob, even though I'm really this: 'MyStruct(" + str(self.some_data) + ", " + str(self.more_data) + ")'"
fn main():
print(greet("world"))
print(greet(False))
var x = MyStruct(5, True)
print(greet(x))
Result:
Hello, world!
Heya! 'n' was False!
Hello, Call me Bob, even though I'm really this: 'MyStruct(5, True)'!
Read more about Stringable here:
https://docs.modular.com/mojo/manual/traits#the-intable-and-stringable-traits
Of note: this answer is current as of Mojo nightly, version 2024.5.1515 (077049dc). The language is still evolving; subtle changes could occur between this post and any future reader.
3 Comments
Alex Craft
Thanks, although I find this
fn greet[T: Stringable](name: T) -> String: and this str(name) a very inconvenient, the need to use a) interface (Stringable), 2) generics and 3) casting, just to handle a simple string, not good...
Dimitri
It is worth noting that you don't have to use the trait or parametric functions. I was demonstrating the ability to build more flexible function that allows use by any Stringable constructs, including those you might not anticipate at the time you are designing the function. Traits allow that type of "build for what you do not know" design. We could have a lengthy conversation about the subject in Modular's Discord, Mojo channel: discord.com/channels/1087530497313357884/1151418092052815884
Dimitri
re casting via
str(name): I believe that the core team plans to add more implicit type casting. Just keep in mind that Mojo is still really new right now and a lot of core language design is still in progress.