Why Does Go Return 'cannot take the address of' or 'cannot call pointer method on' Errors When Chaining Methods?

Understanding Pointer-Related Errors in Go

In Go, you may encounter errors such as "cannot take the address of" and "cannot call pointer method on" when working with pointers. This question and answer explores the reasons behind these errors and provides possible workarounds.

Let's consider the following code that compiles and works:

diff := projected.Minus(c.Origin)
dir := diff.Normalize()

However, if we try to combine the two operations into a single line:

dir := projected.Minus(c.Origin).Normalize()

we will encounter the aforementioned errors. To understand why, we need to delve into the receiver types and addressability of values in Go.

Pointer Receiver and Addressability

The Normalize() method of Vector3 has a pointer receiver (*Vector3), indicating that it requires a pointer to Vector3 value to be called. When you use the shortcut diff.Normalize(), the compiler automatically takes the address of the diff variable (&diff) to match the required pointer receiver type.

However, in the second example, diff.Minus(c.Origin) returns a Vector3 value, which is not addressable. This means the compiler cannot take its address to pass to Normalize().

Workarounds for Pointer Receiver and Addressability

There are several possible workarounds for this issue:

• Assign to a variable and call the method separately: Store the result of Minus() in a variable and then call Normalize() on that variable.
• Create a helper function with a pointer return type: Implement a helper function that returns a pointer to the input Vector3, allowing you to directly call Normalize() on the return value.
• Modify method receiver and result types: Change the receiver of Normalize() to a value receiver (Vector3) and the return type to a pointer (*Vector3).
• Use a method that returns a pointer: Implement a method in Vector3 that returns a pointer to itself, which can then be used to call Normalize().

Additional Points to Consider

• Remember that pointer receivers allow methods to modify the receiver, while value receivers do not.
• Consistent use of pointer/value receivers and result types is recommended for code consistency.
• In the case of simple types like Vector3, there are typically no significant performance concerns with using pointers.

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