best practice append

main.go

// A constructor for a piece of middleware.
// Some middleware use this constructor out of the box,
// so in most cases you can just pass somepackage.New
type Constructor func(http.Handler) http.Handler

// Chain acts as a list of http.Handler constructors.
// Chain is effectively immutable:
// once created, it will always hold
// the same set of constructors in the same order.
type Chain struct {
	constructors []Constructor
}

// New creates a new chain,
// memorizing the given list of middleware constructors.
// New serves no other function,
// constructors are only called upon a call to Then().
func New(constructors ...Constructor) Chain {
	return Chain{append(([]Constructor)(nil), constructors...)}
}