Textual

Built-in trait · Adopted with with Textual

A type that adopts Textual chooses how its values are shown: by print, inside "#{...}", and everywhere else a value becomes text. Without it, a struct is shown field by field, which is the more useful form while a program is being written.

struct Money with Textual {
    const cents: Int

    @override
    func to_string(): String {
        return "$#{self.cents // 100}.#{(self.cents % 100).to_string().pad_start(2, "0")}"
    }
}

print(Money(399))            # prints $3.99
print([Money(399), Money(50)])  # prints [$3.99, $0.50]

The value’s own form is used wherever it appears, even inside a list, a dictionary, or another type’s fields, and it is not put in quotes the way text inside a list is.

to_string(): String

The value as text. print(value) and value.to_string() always give the same text.

Adopting is explicit. A type with a to_string method that does not write with Textual keeps the field-by-field form, and Emerald warns about it.

An enum can adopt Textual too, to show its values in its own words instead of as Weekday.monday.