Keyword: is

The with keyword in Filtrera is used to create a clone of an record with one or more fields overridden. This reference guide provides a detailed specification of the with keyword, focusing on its syntax and usage.

The with keyword allows you to create a new record based on an existing one, with specified fields updated to new values. This cloning mechanism ensures immutability while providing flexibility to modify record fields. Fields can also change type when using the with keyword.

Syntax

Basic Syntax

<new_record> = <existing_record> with { <field1> = <new_value1>, <field2> = <new_value2>, ... }

• <new_record>: The new record created by cloning the existing record.
• <existing_record>: The record to be cloned.
• <field>: The field to be overridden in the new record.
• <new_value>: The new value for the overridden field.

Example

let originalPerson = { name = 'Alice', age = 30 }
let updatedPerson = originalPerson with { age = 31 }

from updatedPerson

In this example, updatedPerson is a clone of originalPerson with the age field updated to 31.

Detailed Syntax

Cloning with Overridden Fields

You can clone an record and override one or more fields to create a new record.

let car = { make = 'Toyota', model = 'Corolla', year = 2020 }
let newCar = car with { year = 2021 }

from newCar

In this example, newCar is a clone of car with the year field updated to 2021.

Changing Field Types

Fields in the new record can also change type when using the with keyword.

let book = { title = 'Filtrera Guide', pages = 300 }
let updatedBook = book with { pages = 'Three Hundred' }

from updatedBook

In this example, updatedBook is a clone of book with the pages field changed from a number to a text.

Cloning with Multiple Field Changes

You can override multiple fields simultaneously.

let employee = { name = 'John', position = 'Developer', salary = 50000 }
let updatedEmployee = employee with { position = 'Senior Developer', salary = 60000 }

from updatedEmployee

In this example, updatedEmployee is a clone of employee with both the position and salary fields updated.

Practical Usage

Example: Updating Nested Records

The with keyword can be used to update fields in nested records.

let company = {
  name = 'Tech Corp',
  location = 'New York',
  ceo = { name = 'Alice', age = 45 }
}

let updatedCompany = company with {
  ceo = company.ceo with { age = 46 }
}

from updatedCompany

In this example, updatedCompany is a clone of company with the age field of the ceo record updated to 46.

Example: Creating Variations of an Record

The with keyword is useful for creating variations of an record without modifying the original.

let product = { name = 'Laptop', price = 1000, inStock = true }
let discountedProduct = product with { price = 900 }
let outOfStockProduct = product with { inStock = false }

from discountedProduct
from outOfStockProduct

In this example, discountedProduct and outOfStockProduct are variations of product with different field values.

Summary

The with keyword in Filtrera provides a powerful mechanism for cloning records with overridden fields, ensuring immutability while allowing flexibility to modify record properties. By understanding its syntax and usage, including changing field types and updating nested records, you can leverage the with keyword to create robust and flexible programs.