Pointers in Wolfram Language

(* Wolfram Language supports references to values and expressions *)

(* We'll show how references work with 2 functions: zeroval and zeroptr *)

(* zeroval takes an integer argument by value *)
zeroval[ival_] := Module[{localVal = ival},
  localVal = 0;
]

(* zeroptr takes a reference to an integer *)
zeroptr[iptr_] := (
  iptr[] = 0;
)

(* Main function *)
Module[{i = 1},
  Print["initial: ", i];
  
  zeroval[i];
  Print["zeroval: ", i];
  
  (* Create a reference to i *)
  iRef = Hold[i];
  
  (* Pass the reference to zeroptr *)
  zeroptr[Function[Null, iRef[[1]], HoldAll]];
  Print["zeroptr: ", i];
  
  (* Print the reference *)
  Print["reference: ", iRef];
]

In Wolfram Language, we don’t have explicit pointers like in some other languages. However, we can achieve similar functionality using references and the Hold attribute.

The zeroval function takes an integer argument by value. It creates a local copy of the argument and sets it to 0, but this doesn’t affect the original value.

The zeroptr function takes a reference to an integer. It uses a pure function with HoldAll attribute to modify the original value.

In the main part of the code:

1. We initialize i to 1 and print its initial value.
2. We call zeroval with i, which doesn’t change the original value of i.
3. We create a reference to i using Hold[i].
4. We pass this reference to zeroptr, which modifies the original value of i.
5. Finally, we print the reference itself.

When you run this code, you’ll see that zeroval doesn’t change the value of i, but zeroptr does, because it has a reference to the original variable.

The output will look something like this:

initial: 1
zeroval: 1
zeroptr: 0
reference: Hold[0]

This demonstrates how Wolfram Language can work with values and references, providing functionality similar to pointers in other languages.