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Mojo trait

Sized

The Sized trait describes a type that has an integer length (such as a string or array).

Any type that conforms to Sized or SizedRaising works with the built-in len() function.

The Sized trait requires a type to implement the __len__() method. For example:

@value
struct Foo(Sized):
    var length: Int

    fn __len__(self) -> Int:
        return self.length
@value
struct Foo(Sized):
    var length: Int

    fn __len__(self) -> Int:
        return self.length

You can pass an instance of Foo to the len() function to get its length:

var foo = Foo(42)
print(len(foo) == 42)
var foo = Foo(42)
print(len(foo) == 42)
True
True

Note: If the __len__() method can raise an error, use the SizedRaising trait instead.

Implemented traits​

AnyType

Methods​

__len__​

__len__(self: T) -> Int

Get the length of the type.

Returns:

The length of the type.

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