Dojo: The Provable Game Engine

Commands

Understanding commands is key to understanding Dojo. You will leverage them heavily within the systems you design.

Commands in Dojo are generalized functions that are expanded at compile time to facilitate system execution. They provide a convenient way for systems to interact with the world state by abstracting common operations, such as retrieving or updating components, and generating unique IDs. By leveraging these commands, developers can streamline their system implementations and improve code readability.

Using commands

Commands are used within systems to interact with the world state. They are called using the following syntax:

let (position, moves) = get!(ctx.world, ctx.origin, (Position, Moves));

The get! command

The get! command is used to retrieve components from the world state.

Use it like this:

let (position, moves) = get!(ctx.world, ctx.origin, (Position, Moves));

Here we are retrieving the Position and Moves components from the world state. We are also using the ctx.origin to retrieve the components for the current entity.

You can then use position and moves as you would as any other Cairo struct.

The set! command

The set! command is used to update components state.

Use it like this:

set !(ctx.world, (
    Moves {
        player: ctx.origin, remaining: 10
    }, 
    Position {
        player: ctx.origin, x: position.x + 10, y: position.y + 10
    },
));

// If the structs are already defined it can also be written as:
set!(ctx.world, (moves, position));

Here we are updating the Moves and Position components in the world state using the ctx.origin as the entity id.

The emit! command

The emit! command is used to emit custom events.

Use it like this:

emit !(ctx.world, Moved { address: ctx.origin, direction });