In fastn there is a concept of or-type can be used when give you a way of saying a value is one of a possible set of values. Consider we are defining shapes, and a shape can be either a rectangle, a circle or a triangle.

-- or-type shape:

-- record rectangle:
decimal width:
decimal height:

-- record triangle:
decimal ab:
decimal bc:
decimal ca:

-- record circle:
decimal radius:

-- end: or-type


This type is loosely equivalent to Rust's enum and is also known as an
[algebraic data type](https://en.wikipedia.org/wiki/Algebraic_data_type).

Lang:

ftd

⚠️

Work in Progress

Currently we can declare a new or-type but can not use our custom or types. Only the builtin or-types defined in built-in can be used by the kernel components.

We are working on a match statements that will enable you to use this type in the future. Checkout our github discussion to know more.

Declaring an `or-type`

An or-type type is declared using the or-type keyword followed by the name of the type. The syntax for the or-type declaration is as follows:

or-type

-- or-type worker:

;; Anonymous Record
-- record individual:
caption name:
string designation:

;; Regular variant, defined using existing type, here we have used `string`
-- string ceo:

;; Constant
-- constant string bot: BOT

-- end: worker

Lang:

ftd

Illustration: Using an `or-type`

To understand the or-type, let's consider an example of a sales business that wants to get "leads". A lead can either be an individual or a company, where individuals have fields like their name and phone number, and companies have fields like company name, name of contact, and fax number.

To create an or-type, we can use the following syntax:

-- or-type lead:

-- record individual:
caption name:
string phone:

-- record company:
caption name:
string contact:
string fax:

-- end: lead

Lang:

ftd

Here, we used ftd::p1's "sub-section" to represent each possibility.

The declarations individual or company are called or-type variants, and they use similar syntax as record declarations. These type of variant is called Anonymous Record.

Types of Variant

The or-type variants are of three types:

Anonymous Record
Regular
Constant

Anonymous Record

An Anonymous Record variant declares a record with fields, similar to a record declaration. However, the fields are defined directly within the or-type declaration. It is called anonymous because there is no pre-defined record type that exists for this variant.

For example, the individual variant in the lead or-type declaration is an Anonymous Record variant:

-- record individual:
caption name:
string phone:

Lang:

ftd

The individual variant has no predefined type, but a record is created on the spot, which becomes the type for the individual variant.

We can use this type to declare variables like this:

Variable initialization

-- lead.individual john: John Doe
phone: 9999999999

-- lead.company my-company: My Company
contact: 9999999999
fax: 7368632

Lang:

ftd

In this example, we have declared two variables of type lead, where john is of variant individual and my-company is of variant company. We then provide values for their respective fields.

Regular

A Regular variant declares any defined type and expects the value provided of that type. It uses a similar syntax to a variable declaration, where we specify the name of the variant and the expected data type.

Consider the following example of a length type declaration:

Regular

-- or-type length:

-- integer px:
-- decimal percent:

-- end: length

Lang:

ftd

Here, both variants, px and percent, are of regular type. i.e. They expect values of the provided type when declaring a variable, field, or component property.

We can use this type to declare variables like this:

Regular

-- length.px pixel-length: 100

-- length.percent percent-length: 10

Lang:

ftd

In this example, we declared two variables of type length, where pixel-length is of variant px that accepts an integer type value, and percent-length is of variant percent that accepts a decimal type value.

Constant

A Constant variant is similar to a Regular variant, but it expects a constant value rather than a variable value. We use the constant keyword to define this variant.

Consider the following example of type declaration:

Constant

-- or-type weekday:

-- constant string sunday: Sunday
-- constant string monday: Monday
-- constant string tuesday: Tuesday
-- constant string wednesday: Wednesday
-- constant string thursday: Thursday
-- constant string friday: Friday
-- constant string saturday: Saturday

-- end: weekday

Lang:

ftd

In this example, we declare an or-type called weekdays with seven variants. Each variant is a Constant of type string, with a fixed value.

We can use this type to declare variables like this:

Constant

-- weekday today: monday

Lang:

ftd

In this example, we declared a variable today of type weekday with monday as variant.

Conclusion

In conclusion, or-type is a way to create an enumeration of variants in fastn programming. It allows you to define a list of possible variants, each with its own set of fields, and then use those variants in your code. or-type variants can be of three types: Anonymous Record, Regular, and Constant.

You can use or-type in situations where you need to choose a value from a set of predefined variants. For example, when working with data that has multiple possible formats or when you need to define a set of constants for your application.

Benefits

Some benefits of using or-type include:

Clear and concise code: or-type allows you to define a set of variants in a single place, making your code more organized and easier to read.
Type safety: By defining the possible variants upfront, you can ensure that your code only accepts values of the correct type, reducing the risk of runtime errors.
Flexibility: or-type variants can have their own set of fields, which allows you to define complex data structures with ease.