Cloning a Component

Sometimes the data you want is already sitting on another Entity: a prototype crate, a buff the player just picked up, a position you want to stamp onto a bullet. Concord lets you pass that instance to give (or ensure) instead of repeating the populate arguments.

A template

local Prototype = world:newEntity()
  :give("position", 10, 20)
  :give("health", 5)

local Drop = world:newEntity()
Drop:give(Prototype.health)   -- copies { hp = 5 }, not a shared table
Drop:give("position", 100, 80)

give(Prototype.health) copies through serialize and deserialize. Populate arguments are ignored: the instance is the source.

Use this when the interesting values already exist. Use an assemblage when you are describing a kind of Entity from arguments (asCat(x, y)).

ensure with an instance is “copy this unless they already have one”:

crate:ensure(Prototype.health)

What will not copy

If serialize returns nil, there is nothing to copy. The builtin serializable flag does that on purpose — it is a marker, not data. A Component that holds a LÖVE Body and returns nil from serialize cannot be cloned this way until you teach it to round-trip. Serialization is that article.

The default serialize is a shallow copy. Nested tables are shared between the original and the clone. If inventory.slots is a table, both Entities will see the same slots until you write a deeper serialize.

Replacing an existing Component still runs removed with replaced == true on the old instance. Cleanup on the source Entity is not your problem; cleanup on the target is, if it already had that name.

See also

• Entity:give
• Serialization
• Entities Guide