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--- en:toolworks:docs:apparatus:subject [2021/12/04 20:29] – [Low-level Subjects] vladius
+++ en:toolworks:docs:apparatus:subject [2021/12/06 22:34] – [C++ Workflow] vladius
@@ Line 1: / Line 1: @@
-====== Subjects. Low-Level Entities ======
+====== Subjects. The Low-Level Entities ======
 //Subjects// are the foundational lightweight entities managed by Apparatus. They are mostly UE-independent and consist of [[en:toolworks:docs:apparatus:trait|Traits]] and [[en:toolworks:docs:apparatus:flagmark|Flags]].
+====== Subject Handles ======
+Subjects are not used directly and their internals are hidden deep from the framework user's perspective. Instead a special concept called //Subject Handle// is introduced. It's really much like a [[ue>ProgrammingAndScripting/ProgrammingWithCPP/UnrealArchitecture/SmartPointerLibrary/WeakPointer|weak pointer]] in terms of Unreal. When you despawn a Subject all of the handles that are currently referencing it become automatically invalid. Internally this is managed through a generation-based referencing technique.
+====== Subjective Layer ======
+A Subject can have an additional higher-level dimension called [[en:toolworks:docs:apparatus:subjective|Subjective]]. Subjectives are UE-managed objects (UObjects) which may contain the high-level [[en:toolworks:docs:apparatus:detail|Details]] in their composition. Subjectives with Details are generally more flexible and have additional features implemented as compared to raw Subjects with Traits. This comes at a cost of being not as memory-/cache-efficient and potentially less performant. Please note however, that the Subjective layer is optional and you may establish your project's logic entirely on Subjects if you want.
+Subjects without the Subjective layer involved are called //barebone// Subjects. Both Subjective-based Subjects and barebone Subjects are commonly referred to as just //Subjects//. That's because every Subjective is actually a Subject internally and embeds it as an essential part. This is something like an inheritance, so every Subjective can also have Traits and Flags as part of its composition.
 ====== Spawning ======
+//Spawning// is a process of creating a Subject as part of a Mechanism.
+===== C++ Workflow =====
+In order to spawn a new Subject within the Mechanism, you should call one of the [[appi>class_a_mechanism.html#a6a4cad7d03e86cc6c32b0bb27780a71d|SpawnSubject]] methods. The simplest one would be:<code cpp>
+FSubjectHandle Subject = Machine::SpawnSubject();
+</code>
+If you want to spawn a Subject with some Traits initially attached to it, use the special templated version of the method:<code cpp>
+FBurning Burning{10, 15.5f};
+FSword Sword{2};
+FSubjectHandle BurningSword = Machine::SpawnSubject(Burning, Sword);
+</code>
+This would efficiently pre-allocate a Slot for the Subject in the correct Chunk and initialize it according to the Traits supplied as the arguments.
+===== Blueprint Workflow =====
+Spawning Subjects in Blueprints is done with a dedicated Spawn Subject node:
+{{:en:toolworks:docs:apparatus:spawn-subject-node.png?nolink|Spawn Subject Node}}
+====== Despawning ======
+The //despawning// process is exactly the opposite of spawning and basically means destroying of a Subject. Destroying an already despawned (or invalid) Subject Handle is a legal operation that does nothing and reports no errors.
 ===== C++ Workflow =====
+In order to destroy a Subject in your C++ code, use the [[appi>struct_f_subject_handle.html#ada8e65dcf50ee385748d6de603ccd4e4|Despawn]] method provided by the Handle structure. Do it like so:<code cpp>
+void PickPowerup(FSubjectHandle Player, FSubjectHandle Powerup)
+{
+  // Add health/energy/strength to the player...
+  ...
+  // Remove the item from the world:
+  Powerup.Despawn();
+}
+</code>