Add test for ExtendExpect

scan/scan.go

@@ -25,21 +25,27 @@ import (
 	"github.com/rwxrob/bonzai/scan/tk"
 )
 
-// ExtendExpect provides a hook to support additional custom scannable
-// support to both the Expect and Check Scanner methods. Take note of
-// the ErrorExpected errors in order to construct similar errors where
-// returning ErrorExpected itself would not provide clear error
-// messages.
-var ExtendExpect func(s *Scanner, scannable ...any) (*Cur, error)
-
 // Scanner implements a non-linear, rune-centric, buffered data scanner.
 // See New for creating a usable struct that implements Scanner. The
 // buffer and cursor are directly exposed to facilitate
 // higher-performance, direct access when needed.
 type Scanner struct {
-	Buf     []byte
-	Cur     *Cur
+
+	// Buf is the data buffer providing infinite look-ahead and behind.
+	Buf []byte
+
+	// Cur is the active current cursor pointing to the Buf data.
+	Cur *Cur
+
+	// Snapped contains the latest Cur when Snap was called.
 	Snapped *Cur
+
+	// ExtendExpect provides a hook to support additional custom
+	// scannables for both Expect and Check Scanner methods. Take note of
+	// the ErrorExpected errors in order to construct similar errors where
+	// returning ErrorExpected itself would not provide clear error
+	// messages.
+	ExtendExpect func(s *Scanner, scannable ...any) (*Cur, error)
 }
 
 // New returns a newly initialized non-linear, rune-centric, buffered
@@ -357,8 +363,8 @@ func (p *Scanner) Expect(scannables ...any) (*Cur, error) {
 			p.Scan()
 
 		default: // --------------------------------------------------------
-			if ExtendExpect != nil {
-				return ExtendExpect(p, scannables...)
+			if p.ExtendExpect != nil {
+				return p.ExtendExpect(p, scannables...)
 			}
 			return nil, fmt.Errorf("expect: unscannable type (%T)", m)
 		}

scan/scan_test.go

@@ -327,7 +327,16 @@ func ExampleExpect_in_Range() {
 }
 
 func ExampleExtendExpect() {
-	// TODO
+	s, _ := scan.New("some thing")
+	s.ExtendExpect = func(s *scan.Scanner, a ...any) (*scan.Cur, error) {
+		return s.Cur, fmt.Errorf("custom error for type %T handled at %v",
+			a[0], s.Cur,
+		)
+	}
+	_, e := s.Expect([]byte{'0'})
+	fmt.Println(e)
+	// Output:
+	// custom error for type []uint8 handled at U+0073 's' 1,1-1 (1-1)
 }
 
 func ExampleSnap() {