Entities

Can be thought of as simply an index to retrieve data associated with the Entity from Components or a Ledger. In the case of a Ledger it will return an EntityState that holds references to all the Components for which the Entity has data.

An Entity should always first be created from an AbstractLedger by using Entity(ledger, comps...) before it is used.

Example

e = Entity(ledger, Comp1(), Comp2())
ledger[e] # EntityState with references to easily retrieve e's data for Comp1 and Comp2

ledger[Comp2][e] # access the Comp2 data of e
ledger[e][Comp2] # identical to above

Combination of an Entity and a bunch of Components for which the Entity has data. It can thus be used as an index similar to a standard Entity, but it also provides some nice ways to retrieve the data associated with it in the Components.

Example

@component struct Comp1
    comp1
end

@component mutable struct Comp2
    comp2
end

@component struct Comp3
    comp3
end    


for e in @entities_in(ledger, Comp1 && Comp2)
    # e is an EntityState
    # we can directly access the fields of Comp1 and Comp2 since they have unique names,
    # and assign a Comp3 to the Entity that's represented by the EntityState
    
    ledger[Comp3][e] = Comp3(e.comp1 + e.comp2)
    # If there are components that have the same name in the EntityState you can access them directly
    e[Comp1].comp1
    e[Comp2].comp2

    # If the Components are mutable we can also set their fields using
    e.comp2 = 3
end

entity(c, i)

Return the EntityState with the ith Entity and data in Component c.

last_entity(c::AbstractComponent)

Retrieves the last Entity in c.