Initialization and execution order

Forms that compile (7)

Syntax	Description
private int V;	No initializer
private int A = 1;	Declaration with initializer
private int B = 2 + 3;	Initialization by expression
private int V = Max;	Using a constant in an initializer
private static int V = 7;	Initializing a static field
private int[] A = new int[3];	Initializing an array
new Point()	Default value of a struct

Forms that don’t compile (2)

Syntax	Description	Error	Reason	Instead
static C() { V = 7; }	Static constructor	TUKI0001	runtime	Put it in a field initializer or Start
[ModuleInitializer] static void Init()	Module initializer	TUKI0001	runtime	Same as above
Both static constructors and module initializers assume a mechanism that runs once, when the type is first used or loaded. The runtime has nothing that triggers that one-time run.

Put initialization in a field initializer or Start.

Field initializers

No initializer

A field without an initializer starts at its default value (0 for int).

using UnityEngine;
using Tsukimi;

public class InNoInit : TsukimiBehaviour
{
    void Start()
    {
        Debug.Log(V);   // => 0
    }

    private int V;
}

Declaration with initializer

using UnityEngine;
using Tsukimi;

public class InFieldOrder : TsukimiBehaviour
{
    void Start()
    {
        Debug.Log(B);   // => 2
    }

    private int A = 1;
    private int B = 2;
}

Initialization by expression

using UnityEngine;
using Tsukimi;

public class InFieldExpr : TsukimiBehaviour
{
    void Start()
    {
        Debug.Log(B);   // => 5
    }

    private int A = 1;
    private int B = 2 + 3;
}

Using a constant in an initializer

using UnityEngine;
using Tsukimi;

public class InConstFirst : TsukimiBehaviour
{
    void Start()
    {
        Debug.Log(V);   // => 10
    }

    private const int Max = 10;
    private int V = Max;
}

Initializing a static field

using UnityEngine;
using Tsukimi;

public class InStaticFieldInit : TsukimiBehaviour
{
    void Start()
    {
        Debug.Log(V);   // => 7
    }

    private static int V = 7;
}

Initializing an array

using UnityEngine;
using Tsukimi;

public class InArrayFieldInit : TsukimiBehaviour
{
    void Start()
    {
        Debug.Log(A.Length);   // => 3
    }

    private int[] A = new int[3];
}

Default values

Default value of a struct

A struct created with new starts with all fields at their default values.

using UnityEngine;
using Tsukimi;

public struct Point { public int X; }
public class InStructDefault : TsukimiBehaviour
{
    void Start()
    {
        Point p = new Point();
        Debug.Log(p.X);   // => 0
    }
}