Why Can't I Call a Pointer Method on the Result of a Go Function Call?

Understanding "Cannot Take the Address Of" and "Cannot Call Pointer Method On" Errors

When working with Go, one may encounter errors such as "cannot take the address of" or "cannot call pointer method on," confusing those learning the language.

The Issue:

Consider the following Go code:

diff := projected.Minus(c.Origin)
dir := diff.Normalize() // error: cannot call pointer method on Vector3

// Vector3 methods
func (a *Vector3) Minus(b Vector3) Vector3 { ... }
func (a *Vector3) Normalize() Vector3 { ... }

The second line causes compilation errors because Vector3.Normalize() requires a pointer receiver, meaning it expects a pointer to a Vector3 value (*Vector3) instead of a Vector3 value.

Why it Happens:

Return values of function and method calls are not addressable in Go. Therefore, in the second example, the compiler cannot take the address of the result of Vector3.Minus(), preventing it from calling Normalize() on that value.

Possible Solutions:

• Separate Assignment: Assign the return value to a variable and call the method on that variable, as seen in the first example where dir = diff.Normalize() works.
• Change Receiver Type: Modify the Normalize() method to have a value receiver (Vector3 instead of *Vector3). This allows chaining method calls on non-pointer values.
• Return Pointers: Make Normalize() return a pointer (*Vector3) to avoid the need for addressing the return value.
• Create a Helper Function: Create a function to return the address of a value, such as pv(v) to return &v, and call Normalize() on its result.

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