When to Use Pointers vs Values in Go

Use values for small, immutable types like int or string to avoid copying overhead, and use pointers for large structs or when you need to modify the original data. In the gmp example, Int is a struct wrapping C.mpz_t, so methods like Set take *Int to modify the underlying C memory directly without copying the entire struct.

// Value: small, immutable, copied on pass
func Add(a, b int) int { return a + b }

// Pointer: large struct or needs modification
func (z *Int) Set(x *Int) *Int {
	z.doinit()
	C.mpz_set(&z.i[0], &x.i[0])
	return z
}

Think of passing a value like handing someone a photocopy of a document; they can read it, but changes they make won't affect your original. Passing a pointer is like handing them the original document; any changes they make are permanent. You use pointers for big things to save time copying them, or when you need the receiver to change the actual data.