Class Arrays need to be allocated

Monkey Forums/Monkey Programming/Class Arrays need to be allocated

AdamRedwoods

(Posted 2012) [#1]

I couldn't find any reference to this subject, but never really thought why this is so:

Class Other
   Field x:Int
End

Local a:Other[] = New Other[10]

a[5].x = 10 ''segmentation error

but yet it's ok with built-in types.

Question 2:
is there an easy way to allocate object arrays? I assume not and we have to allocate object arrays in a for/next loop.

doing

a = a[0..10]

does not work either.

Jesse

(Posted 2012) [#2]

you need to initialize(create) each object. this is actually good because it won't use up memory unless you create the individual objects and makes arrays quite flexible.


Class Other
    Field x:int
End

Local a:Other[] = New Other[10] ' allocate pointers for 10 objects

For Local i:int = 0 until 10
    Other[i] = new Other ' assign new object to pointer
next 

a[5].x = 10

I am sure you can think of a way to automate it for your needs.

AdamRedwoods

(Posted 2012) [#3]

right, automate it with the class:

Class Other
	Field x:Int
	
	Function AllocateArray:Other[](i:Int=0)
		Local o:Other[i]
		For Local j:= 0 To i-1
			o[j] = New Other
		Next
		Return o
	End
End

But I guess my assumption that the memory was allocated, looking at the resulting cpp code:

Array<bb_androidtest_Other* > t_a=Array<bb_androidtest_Other* >(10);

And the Array cpp class does a memset in the constructor.... or so I think. This is why I question why it gives me a seg fault?

EDIT:
I would have assumed this allocates pointers:
Local a:Other[10]
...and this would allocate object memory:
Local a:Other[] = New Other[10]

Jesse

(Posted 2012) [#4]

I have always thought of "New Object[n]" as a way to create a new array size.
I am not too familiar with cpp but if it creates arrays like c than it's handling the objects in the same way Monkey is.

NoOdle

(Posted 2012) [#5]

a = a[0..10]

does not work either.

If you want to resize an array try array.Resize( x )... not sure if thats what you mean

Samah

(Posted 2012) [#6]

I would have assumed this allocates pointers:
Local a:Other[10]
...and this would allocate object memory:
Local a:Other[] = New Other[10]

These are essentially the same thing.
Instantiating an array only creates the space for the pointers. You still need to instantiate each object and assign them to the array indices.

Gerry Quinn

(Posted 2012) [#7]

Class Other
   Field x:Int
End

In C++, an instance of Other would basically be an int, and New Other[10] would return a pointer to an array of ten ints.

In Monkey, Other is an object that contains an int. In other words the array of Others consists of ten pointers to instances of Other objects. The pointers aren't valid until the objects are allocated.