Value

val Value: object?

Declaring type: Optional<T>
Namespace: System
Assembly: Raven.Core.dll
Source file: Optional.rvn

Represents an available value (Some) or meaningful absence (None). Use Optional<T> when having no value is an ordinary outcome. Use Result<T, E> when the caller needs a reason for failure.

Usage

Handle cases with if ... else

A profile form can leave its nickname field blank. This function trims the input and makes that absence explicit instead of using an empty string as a special value. The if ... else expression produces the optional value.

import System.*
import System.Optional.*

func ReadNickname(input: string) -> Optional<string> {
    let name = input.Trim()
    return if name.Length == 0 {
        None
    } else {
        Some(name)
    }
}

let nickname = ReadNickname(" Ada ")
if nickname is Some(let displayName) {
    Console.WriteLine("Welcome, ${displayName}!")
} else {
    Console.WriteLine("Welcome, guest!")
}
// Welcome, Ada!

Some(let displayName) both checks the case and binds its value. displayName is available only in the successful branch; the else branch handles None.

Extract a value or use a fallback with if let

Continuing the profile example, a heading needs a string in both cases. An if let expression binds the nickname when present and supplies a fallback when absent. Both branches compute the heading rather than performing an action.

let heading = if let Some(profileName) = ReadNickname("   ") {
    "Profile: ${profileName}"
} else {
    "Guest profile"
}
Console.WriteLine(heading)
// Guest profile

Propagate None with ?

A profile handle can be created only when a nickname exists. Here ? extracts the string from Some, or immediately returns None from CreateHandle. The remaining code runs only when there is a name. Wrap the final value in Some to return a successful optional result.

func CreateHandle(input: string) -> Optional<string> {
    let name = ReadNickname(input)?
    Some("@${name.ToLowerInvariant()}")
}

let handle = CreateHandle(" Ada ") // Some("@ada")
let missing = CreateHandle("   ") // None
Console.WriteLine(handle.UnwrapOr("guest"))
Console.WriteLine(missing.UnwrapOr("guest"))
// @ada
// guest

Choose an explicit branch when this function should provide a fallback or take a different action. Use ? when absence should remain absence for its caller. A match expression is also available when you want to handle both cases exhaustively.

Type parameters

Property value

Object?