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Kavachकवच

Records

Also known as: struct class object union enum variant pattern matching match switch case tagged immutable update copy

● Intermediate5 minBefore this: Data Types, FunctionsSpec 2.4

A record is a type of your own: named fields grouped under one name, such as a User with a name and an age.

Syntax

type Name {
    field: Type
    other: Type = default
}
syntax: Kavach code

Example

type User {
    name: String
    age: Int
    city: String = "Pune"
}

fn main() {
    const asha = User(name: "Asha", age: 31)
    print("{asha.name}, {asha.age}, {asha.city}")
    const older = asha with { age: 32 }
    print("{asha.age} -> {older.age}")
    let copy = asha
    copy.city = "Delhi"
    print("{asha.city} / {copy.city}")
}

The program ran and printed:

kavach run record.kav

Asha, 31, Pune31 -> 32Pune / Delhi
record.kav: Kavach code, then what running it prints
  • type User { … } declares the record; User(name: …, age: …) makes one, naming every field.
  • asha.name reads a field.
  • A record is a value: copy changing its city leaves asha as she was.

Other languages call this a struct, or a class with only data.

One page for each form

Declaring →Default values →Updating with with →

Try it yourself

Declare a Book with a title and a number of pages, make one, and print its title.
Show the answer

type Book { title: String pages: Int } (one field per line), then const b = Book(title: "Gitanjali", pages: 103) and print(b.title).

What Kavach does for you

  • Small records live in registers

    A record nobody else holds needn't be built in memory at all: its fields can stay in CPU registers.

    sroa.rs