add support for defining an "eponymous only" virtual table (#885)

* add support for defining an "eponymous only" virtual table

As suggested here: https://github.com/mattn/go-sqlite3/issues/846#issuecomment-736206222

* add an example of an eponymous only vtab module

* add a test case for an eponymous only vtab module

1 files changed, 118 insertions, 0 deletions

diff --git a/_example/vtable_eponymous_only/vtable.go b/_example/vtable_eponymous_only/vtable.go
new file mode 100644
index 0000000..49fc0b7
--- /dev/null
+++ b/_example/vtable_eponymous_only/vtable.go
@@ -0,0 +1,118 @@
+package main
+
+import (
+	"fmt"
+
+	"github.com/mattn/go-sqlite3"
+)
+
+type seriesModule struct{}
+
+func (m *seriesModule) EponymousOnlyModule() {}
+
+func (m *seriesModule) Create(c *sqlite3.SQLiteConn, args []string) (sqlite3.VTab, error) {
+	err := c.DeclareVTab(fmt.Sprintf(`
+		CREATE TABLE %s (
+			value INT,
+			start HIDDEN,
+			stop HIDDEN,
+			step HIDDEN
+		)`, args[0]))
+	if err != nil {
+		return nil, err
+	}
+	return &seriesTable{0, 0, 1}, nil
+}
+
+func (m *seriesModule) Connect(c *sqlite3.SQLiteConn, args []string) (sqlite3.VTab, error) {
+	return m.Create(c, args)
+}
+
+func (m *seriesModule) DestroyModule() {}
+
+type seriesTable struct {
+	start int64
+	stop  int64
+	step  int64
+}
+
+func (v *seriesTable) Open() (sqlite3.VTabCursor, error) {
+	return &seriesCursor{v, 0}, nil
+}
+
+func (v *seriesTable) BestIndex(csts []sqlite3.InfoConstraint, ob []sqlite3.InfoOrderBy) (*sqlite3.IndexResult, error) {
+	used := make([]bool, len(csts))
+	for c, cst := range csts {
+		if cst.Usable && cst.Op == sqlite3.OpEQ {
+			used[c] = true
+		}
+	}
+
+	return &sqlite3.IndexResult{
+		IdxNum: 0,
+		IdxStr: "default",
+		Used:   used,
+	}, nil
+}
+
+func (v *seriesTable) Disconnect() error { return nil }
+func (v *seriesTable) Destroy() error    { return nil }
+
+type seriesCursor struct {
+	*seriesTable
+	value int64
+}
+
+func (vc *seriesCursor) Column(c *sqlite3.SQLiteContext, col int) error {
+	switch col {
+	case 0:
+		c.ResultInt64(vc.value)
+	case 1:
+		c.ResultInt64(vc.seriesTable.start)
+	case 2:
+		c.ResultInt64(vc.seriesTable.stop)
+	case 3:
+		c.ResultInt64(vc.seriesTable.step)
+	}
+	return nil
+}
+
+func (vc *seriesCursor) Filter(idxNum int, idxStr string, vals []interface{}) error {
+	switch {
+	case len(vals) < 1:
+		vc.seriesTable.start = 0
+		vc.seriesTable.stop = 1000
+		vc.value = vc.seriesTable.start
+	case len(vals) < 2:
+		vc.seriesTable.start = vals[0].(int64)
+		vc.seriesTable.stop = 1000
+		vc.value = vc.seriesTable.start
+	case len(vals) < 3:
+		vc.seriesTable.start = vals[0].(int64)
+		vc.seriesTable.stop = vals[1].(int64)
+		vc.value = vc.seriesTable.start
+	case len(vals) < 4:
+		vc.seriesTable.start = vals[0].(int64)
+		vc.seriesTable.stop = vals[1].(int64)
+		vc.seriesTable.step = vals[2].(int64)
+	}
+
+	return nil
+}
+
+func (vc *seriesCursor) Next() error {
+	vc.value += vc.step
+	return nil
+}
+
+func (vc *seriesCursor) EOF() bool {
+	return vc.value > vc.stop
+}
+
+func (vc *seriesCursor) Rowid() (int64, error) {
+	return int64(vc.value), nil
+}
+
+func (vc *seriesCursor) Close() error {
+	return nil
+}