[Learning] Should I define methods on values or pointers?
Stack Overflow: https://stackoverflow.com/questions/25382073/defining-golang-struct-function-using-pointer-or-not
Can someone explain to me why appending to an array works when you do this:
func (s *Sample) Append(name string) {
d := &Stuff{
name: name,
}
s.data = append(s.data, d)
}
But not when you do this:
func (s Sample) Append(name string) {
d := &Stuff{
name: name,
}
s.data = append(s.data, d)
}
Is there any reason at all why you would want to use the second example.
Should I define methods on values or pointers?
func (s *MyStruct) pointerMethod() { } // method on pointer
func (s MyStruct) valueMethod() { } // method on value
First, and most important, does the method need to modify the receiver? If it does, the receiver must be a pointer. (Slices and maps act as references, so their story is a little more subtle, but for instance to change the length of a slice in a method the receiver must still be a pointer.)
In the examples above, if pointerMethod modifies the fields of s, the caller will see those changes, but valueMethod is called with a copy of the caller's argument (that's the definition of passing a value), so changes it makes will be invisible to the caller.
In your case, func (s Sample) Append(name string) modifies a copy.
laher reminds us in the comments that using a value instead of pointer also means getting a copy, and respecting the immutable nature of an object:
You'd want to use the non-pointer valueMethod when (for nstance) you're returning a [value derived from an] 'immutable' private property.
See "Why are receivers pass by value in Go?":
Can be useful if for instance you have a small immutable object. The caller can know for certain that this method doesn't modify it's receiver. They can't know this if the receiver is a pointer without reading the code first.
Medium: When to use pointers in Go