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Props

A prop is special type of property that can store a value on an entity. It differs from a field in that it signals when it changes.

pub prop hero.Health
pub fn hero.Example() {
    Health = 100
    with Health {
        Transmission { "Health: " + Health }
    }
    Health = 75
}
// Outputs "Health: 100" then "Health: 75"

Declaration​

Every prop must have a subject parameter. The subject designates the entity on which the value will be stored. The subject parameter can be any identifier beginning with a lowercase letter, or World to make a global prop. When accessing the prop, the subject will be found implicitly from context if not specified explicitly.

The prop's name must begin with an uppercase letter.

prop hero.Health
prop World.NumBananas

Props can be declared as public using the pub keyword, which allows them to be accessed from all files in the program. Otherwise, they are private and can only be accessed from within the file it is declared within. If two private props have the same name but are in different files, they are not the same prop and will not interfere with each other.

pub prop hero.Health
pub prop World.NumBananas

Working with fields​

Reading a prop using its name.

let value = Health // implicit subject (recommended)
let value = hero.Health // or explicit subject

Write to a prop by using an assignment statement =.

Health = 100 // implicit subject (recommended)
hero.Health = 100 // or explicit subject

await can be used to wait until a prop changes. The new value of the prop will be returned.

let value = await Health // implicit subject (recommended)
let value = await hero.Health // or explicit subject

Like all other await functions, it is possible to use with, on or once to handle the change.

with Health {
    Transmission { "Health: " + Health }
}

Props can also be deleted to remove their value from memory.

delete Health // implicit subject (recommended)
delete hero.Health // or explicit subject

IDs​

When a prop is declared with an ID, it stores multiple values that can only be accessed when using the same ID. This enables code to be more generic.

The ID may be optional.

pub symbol HeadSlot
pub symbol HandSlot

pub prop hero.Inventory<Id>

pub fn hero.Example() {
    on Inventory<HeadSlot> {
        Transmission { "Head: " + Inventory<HeadSlot> }
    }
    on Inventory<HandSlot> {
        Transmission { "Hand: " + Inventory<HandSlot> }
    }
    
    Inventory<HeadSlot> = $helmetOfWisdom
    Inventory<HandSlot> = $swordOfRighteousness
}
// Outputs "Head: $helmetOfWisdom" then "Hand: $swordOfRighteousness"