Combining trait bounds in Mojo

& joins trait bounds, demanding a type satisfy every one of them.

trait Named:
    def name(self) -> String:
        ...


trait Weighed:
    def kilograms(self) -> Float64:
        ...


@fieldwise_init
struct Crate(ImplicitlyCopyable, Movable, Named, Weighed):
    var label: String
    var mass: Float64

    def name(self) -> String:
        return self.label

    def kilograms(self) -> Float64:
        return self.mass


def manifest[T: Named & Weighed](item: T) -> String:
    return item.name() + " weighs " + String(item.kilograms())


def main():
    print(manifest(Crate("bolts", 12.5)))

How it works

1. Named and Weighed each ask for a single method.
2. Crate lists both traits in its header and implements the pair.
3. manifest[T: Named & Weighed] may then call name() and kilograms() on item.

Keywords and builtins used here

• Float64
• Movable
• String
• def
• kilograms
• main
• manifest
• name
• print
• return
• self
• struct
• trait
• var

The run, in numbers

Lines

28

Characters to type

469

Tokens

124

Three-star pace

70 tpm

At the three-star pace of 70 tokens a minute, this run takes about 106 seconds.

Type this snippet

Step 4 of 5 in Traits, step 19 of 22 in Structs & traits.

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