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@implicit

You can add the @implicit decorator on any single-argument constructor to identify it as eligible for implicit conversion.

For example:

struct MyInt:
    var value: Int

    @implicit
    fn __init__(out self, value: Int):
        self.value = value

    fn __init__(out self, value: Float64):
        self.value = int(value)


struct MyInt:
    var value: Int

    @implicit
    fn __init__(out self, value: Int):
        self.value = value

    fn __init__(out self, value: Float64):
        self.value = int(value)


This implicit conversion constructor allows you to pass an Int to a function that takes a MyInt argument, or assign an Int to a variable of type MyInt. However, the constructor that takes a Float64 value is not an implicit conversion constructor, so it must be invoked explicitly:

fn func(n: MyInt):
    print("MyInt value: ", n.value)

fn main():
    func(Int(42))             # Implicit conversion from Int: OK
    func(MyInt(Float64(4.2))) # Explicit conversion from Float64: OK
    func(Float64(4.2))        # Error: can't convert Float64 to MyInt
fn func(n: MyInt):
    print("MyInt value: ", n.value)

fn main():
    func(Int(42))             # Implicit conversion from Int: OK
    func(MyInt(Float64(4.2))) # Explicit conversion from Float64: OK
    func(Float64(4.2))        # Error: can't convert Float64 to MyInt

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