Struct Entity

Identifies an entity.

Namespace: Unity.Entities

Syntax

public struct Entity : IEquatable<Entity>, IComparable<Entity>

Remarks

The entity is a fundamental part of the Entity Component System. Everything in your game that has data or an identity of its own is an entity. However, an entity does not contain either data or behavior itself. Instead, the data is stored in the components and the behavior is provided by the systems that process those components. The entity acts as an identifier or key to the data stored in components.

Entities are managed by the EntityManager class and exist within a World. An Entity struct refers to an entity, but is not a reference. Rather the Entity struct contains an Index used to access entity data and a Version used to check whether the Index is still valid. Note that you generally do not use the Index or Version values directly, but instead pass the Entity struct to the relevant API methods.

Pass an Entity struct to methods of the EntityManager, the EntityCommandBuffer, or the ComponentSystem in order to add or remove components, to access components, or to destroy the entity.

Fields

Index

The ID of an entity.

Declaration

public int Index

Field Value

Type	Description
Int32	The index into the internal list of entities.

Remarks

Entity indexes are recycled when an entity is destroyed. When an entity is destroyed, the EntityManager increments the version identifier. To represent the same entity, both the Index and the Version fields of the Entity object must match. If the Index is the same, but the Version is different, then the entity has been recycled.

Version

The generational version of the entity.

Declaration

public int Version

Field Value

Type	Description
Int32	Used to determine whether this Entity object still identifies an existing entity.

Remarks

The Version number can, theoretically, overflow and wrap around within the lifetime of an application. For this reason, you cannot assume that an Entity instance with a larger Version is a more recent incarnation of the entity than one with a smaller Version (and the same Index).

Properties

Null

A "blank" Entity object that does not refer to an actual entity.

Declaration

public static readonly Entity Null { get; }

Property Value

Type	Description
Entity

Methods

CompareTo(Entity)

Compare this entity against a given one

Declaration

public int CompareTo(Entity other)

Parameters

Type	Name	Description
Entity	other	The other entity to compare to

Returns

Type	Description
Int32	Difference based on the Entity Index value

Equals(Object)

Entity instances are equal if they refer to the same entity.

Declaration

public override bool Equals(object compare)

Parameters

Type	Name	Description
Object	compare	The object to compare to this Entity.

Returns

Type	Description
Boolean	True, if the compare parameter contains an Entity object having the same Index and Version as this Entity.

Overrides

ValueType.Equals(Object)

Equals(Entity)

Entity instances are equal if they represent the same entity.

Declaration

public bool Equals(Entity entity)

Parameters

Type	Name	Description
Entity	entity	The other Entity.

Returns

Type	Description
Boolean	True, if the Entity instances have the same Index and Version.

GetHashCode()

A hash used for comparisons.

Declaration

public override int GetHashCode()

Returns

Type	Description
Int32	A unique hash code.

Overrides

ValueType.GetHashCode()

ToString()

Provides a debugging string.

Declaration

public override string ToString()

Returns

Type	Description
String	A string containing the entity index and generational version.

Overrides

ValueType.ToString()

Operators

Equality(Entity, Entity)

Entity instances are equal if they refer to the same entity.

Declaration

public static bool operator ==(Entity lhs, Entity rhs)

Parameters

Type	Name	Description
Entity	lhs	An Entity object.
Entity	rhs	Another Entity object.

Returns

Type	Description
Boolean	True, if both Index and Version are identical.

Inequality(Entity, Entity)

Entity instances are equal if they refer to the same entity.

Declaration

public static bool operator !=(Entity lhs, Entity rhs)

Parameters

Type	Name	Description
Entity	lhs	An Entity object.
Entity	rhs	Another Entity object.

Returns

Type	Description
Boolean	True, if either Index or Version are different.