module use genericity can not set null

[supemeko]

show a error:

public module Storage<T>
    T t
    function setNull()
        t = null // error: Cannot assign null to int

public class StorageInt
    use Storage<int>

next is correct:

public module Storage<T>
    T t
    function setNull()
        t = null

class Int
    int value

public class StorageInt
    use Storage<Int>

[peq]

This is intended behavior. It is the same as when you write int x = null. The literal null is only valid for object and handle types.

If you need a default value in a module, I suggest that you add an abstract function default() returns T or add another boolean attribute to keep track whether the element is defined or not.

With the planned new generics (#679) it will also be possible to use a type class for this.

[supemeko]

This is intended behavior. It is the same as when you write int x = null. The literal null is only valid for object and handle types.

If you need a default value in a module, I suggest that you add an abstract function default() returns T or add another boolean attribute to keep track whether the element is defined or not.

With the planned new generics (#679) it will also be possible to use a type class for this.

but, It is correct in the a class,

public class Storage<T>
    T t
    construct()
        t = null
    function set(T t)
        this.t = t

enum _enum
    A
    B

function _enumFromIndex(int i) returns _Tuple
    return _Tuple(i.toString())

function _enumToIndex(_enum i) returns int
    return i castTo int

class Class
    int num
    construct(int num)
        this.num = num

tuple _Tuple(string num)

function _TupleFromIndex(int i) returns _Tuple
    return _Tuple(i.toString())

function _TupleToIndex(_Tuple i) returns int
    return i.num.toInt()

@Test function atest()
    let num = new Storage<int>
    num.t.assertEquals(0)

    num.set(2)
    num.t.assertEquals(2)

    let str = new Storage<string>
    str.set("3")
    str.t.assertEquals("3")

    let _class = new Storage<Class>
    _class.set(new Class(4))
    _class.t.num.assertEquals(4)

    let _Tuple = new Storage<_Tuple>
    _Tuple.set(_Tuple("5"))
    _Tuple.t.num.assertEquals("5")

    let __enum = new Storage<_enum>
    __enum.set( _enum.A )
    __enum.t castTo int.assertEquals( _enum.A castTo int )
    __enum.set( _enum.B )
    __enum.t castTo int.assertEquals( _enum.B castTo int )

Even in the standard package LinkedList:

public class LinkedList<T>
	private var dummy = new LLEntry<T>(null, null, null)
	...

class LLEntry<T>
	T elem
	LLEntry<T> prev
	LLEntry<T> next

	construct(T elem, LLEntry<T> prev, LLEntry<T> next)
		this.elem = elem -- set null
		this.prev = prev
		this.next = next