Chapter 6: Pointers

A pointer is an indirect reference to one or more values stored in memory. The pointer is a value that holds an address to memory, and provides APIs to store and retrieve values to that memory. The value pointed to by a pointer is also known as a pointee.

The Mojo standard library includes several types of pointers, which provide different sets of features. All of these pointer types are generic—they can point to any type of value, and the value type is specified as a parameter. For example, the following code creates an OwnedPointer that points to an Int value:

from std.memory import OwnedPointer

var ptr: OwnedPointer[Int]
ptr = OwnedPointer(100)

The ptr variable has a value of type OwnedPointer[Int]. The pointer points to a value of type Int, as shown in Figure 1.

Accessing the memory—to retrieve or update a value—is called dereferencing the pointer. You can dereference a pointer by following the variable name with an empty pair of square brackets:

# Update an initialized value
ptr[] += 10
# Access an initialized value
print(ptr[])