Pattern matching

Use pattern matching to promote an object to its class from one of its traits. Pattern matching can match object contents or value as well.

Warning

Pattern matching is only partly implemented.

Below is the contents of src/main.mys found in the pattern_matching example.

trait Base:
    pass

class Foo(Base):
    a: i64
    b: string

class Bar(Base):
    pass

class Fie(Base):
    pass

func classes(base: Base):
    # Foo() and Bar() just means these classes with any state. No
    # instance is created, just the type is checked.
    match base:
        case Foo(a=1) as foo:
            print(f"Class Foo with a=1 and b=\"{foo.b}\".")
        case Foo(a=2, b="ho"):
            print("Class Foo with a=2 and b=\"ho\".")
        case Foo():
            print("Class Foo.")
        case Bar():
            print("Class Bar.")
        case _:
            print(f"Other class: {base}")

func numbers(value: i64):
    match value:
        case 0:
            print("Zero integer.")
        case 5:
            print("Five integer.")

func strings(value: string):
    match value:
        case "foo":
            print("String foo.")
        case _:
            print(f"Other string: {value}")

func main():
    classes(Foo(1, "hi"))
    classes(Foo(2, "ho"))
    classes(Foo(3, ""))
    classes(Bar())
    classes(Fie())
    numbers(0)
    numbers(1)
    numbers(5)
    strings("foo")
    strings("bar")

Build and run.

❯ mys run
 ✔ Reading package configuration (0 seconds)
 ✔ Building (0.01 seconds)
Class Foo with a=1 and b="hi".
Class Foo with a=2 and b="ho".
Class Foo.
Class Bar.
Other class: Fie()
Zero integer.
Five integer.
String foo.
Other string: bar