Pointer and address memory of x value

[survuvi]

Hello, why I have this error when I try to print the address memory of x?

var x : Int = 42  # x must be mutable

let xPtr = Pointer[Int].address_of(x) # get address memory of x

print(xPtr.address_of()) # print address memory of x

print(xPtr.load()) # dereference the pointer and print value of x

_error: Expression [9]:21:26: invalid call to 'address_of': callee expects 1 argument, but 0 were specified
print(xPtr.address_of()) # print address memory of x

/.modular/Kernels/mojo/Stdlib/Pointer.mojo:103:5: function declared here
fn address_of(inout arg: type) -> Self:_

[DayDun]

address_of is a static method and is not meant to be called on an instance, only on the type itself.

If you want to print the address you probably want to write

var x : Int = 42
let xPtr = Pointer[Int].address_of(x)
print(xPtr.__as_index())
print(xPtr.load())

94602671945872
42

[Moosems]

Which I understand completely. But those often use pointers to variable addresses, why would one need it for the type itself?

[abhinav-upadhyay]

You also need to know the type of the data stored at the location pointed to by the pointer so that you can do anything meaningful with it. For example, if it is a 64 byte signed int stored there, or an 8 bit unsigned int. When you dereference the pointer, the bytes need to be interpreted based on the type.

In case of Mojo they have parameterized it by the type of pointer. For example:

var x : Int = 42
let xPtr = Pointer[Int].address_of(x)

So xPtr is a pointer to an Int with type Pointer[Int].

[survuvi]

@abhinav-upadhyay pointers could be used for AI embeddings too?

[abhinav-upadhyay]

@abhinav-upadhyay pointers could be used for AI embeddings too?

Yes. An embedding is just a vector of floating point numbers. For efficient operations you would want to use a pointer to represent it.

Let's say the size of the embedding is 100, then you would create a pointer of F32 type and allocate memory for storing 100 values starting at that address.

fn create_arr(size: Int) -> DTypePointer[DType.f32]:
    let arr = DTypePointer[DType.f32].alloc(size)
    # write random values to the array but this could be your embeddings as well
    rand[DType.f32](arr, size)
    return arr

The above example taken and modified from my article

[survuvi]

your articles are very interesting, please allow easy copy/paste code instead of images