Ele foi uma das primeiras implementações de um framework usando Python _type hints_ para declarar parâmetros e requisições que eu nunca vi (antes no NestJS e Molten). Eu encontrei ele mais ou menos na mesma época que o Hug. Mas o APIStar utilizava o padrão OpenAPI.

Ele tinha validação de dados automática, serialização de dados e geração de _schema_ OpenAPI baseado nos mesmos _type hints_ em vários locais.

	// run time error if it has a RuntimeError method.
	RuntimeError()
}

// A TypeAssertionError explains a failed type assertion.
type TypeAssertionError struct {
	_interface    *_type
	concrete      *_type
	asserted      *_type
	missingMethod string // one method needed by Interface, missing from Concrete
}

func (*TypeAssertionError) RuntimeError() {}

func (e *TypeAssertionError) Error() string {

}

// makeslicecopy allocates a slice of "tolen" elements of type "et",
// then copies "fromlen" elements of type "et" into that new allocation from "from".
func makeslicecopy(et *_type, tolen int, fromlen int, from unsafe.Pointer) unsafe.Pointer {
	var tomem, copymem uintptr
	if uintptr(tolen) > uintptr(fromlen) {
		var overflow bool
		tomem, overflow = math.MulUintptr(et.Size_, uintptr(tolen))

					// set up with empty interface
					(*eface)(r)._type = &f.ot.Type
					(*eface)(r).data = f.arg
					if len(ityp.Methods) != 0 {
						// convert to interface with methods
						// this conversion is guaranteed to succeed - we checked in SetFinalizer
						(*iface)(r).tab = assertE2I(ityp, (*eface)(r)._type)
					}
				default:
					throw("bad kind in runfinq")
				}

		// treat it as such.
		// 1. If it is a non-empty interface, the pointer points to an itab
		//    which is always in persistentalloc space.
		// 2. If it is an empty interface, the pointer points to a _type.
		//   a. If it is a compile-time-allocated type, it points into
		//      the read-only data section.
		//   b. If it is a reflect-allocated type, it points into the Go heap.

// license that can be found in the LICENSE file.

package runtime

import "internal/abi"

// isDirectIface reports whether t is stored directly in an interface value.
func isDirectIface(t *_type) bool {
	return t.Kind_&abi.KindDirectIface != 0

	// In the allocation headers experiment, we reserve the end of the chunk for
	// a pointer/scalar bitmap. We also reserve space for a dummy _type that
	// refers to the bitmap. The PtrBytes field of the dummy _type indicates how
	// many of those bits are valid.
	return userArenaChunkBytes/goarch.PtrSize/8 + unsafe.Sizeof(_type{})
}

type userArena struct {
	// full is a list of full chunks that have not enough free memory left, and

	Inter   *InterfaceType
	CanFail bool
}
type TypeAssertCache struct {
	Mask    uintptr
	Entries [1]TypeAssertCacheEntry
}
type TypeAssertCacheEntry struct {
	// type of source value (a *runtime._type)
	Typ uintptr
	// itab to use for result (a *runtime.itab)
	// nil if CanFail is set and conversion would fail.
	Itab uintptr

	if GOARCH != "386" {
		// cdecl is only meaningful on 386.
		cdecl = false
	}

	if fn._type == nil || (fn._type.Kind_&abi.KindMask) != abi.Func {
		panic("compileCallback: expected function with one uintptr-sized result")
	}
	ft := (*functype)(unsafe.Pointer(fn._type))

	// Check arguments and construct ABI translation.
	var abiMap abiDesc
	for _, t := range ft.InSlice() {

	dx    uint32 /* ... */
	cx    uint32 /* ... */
	ax    uint32 /* ... */
	gs    uint32 /* data segments */
	fs    uint32 /* ... */
	es    uint32 /* ... */
	ds    uint32 /* ... */
	trap  uint32 /* trap _type */
	ecode uint32 /* error code (or zero) */
	pc    uint32 /* pc */
	cs    uint32 /* old context */
	flags uint32 /* old flags */
	sp    uint32
	ss    uint32 /* old stack segment */
}

type sigctxt struct {