Another try to support custom aggregate functions.

README

 Yet another SQLite binding based on:
  - original [Russ Cox's](http://code.google.com/p/gosqlite/) implementation,
  - the [Patrick Crosby's](https://github.com/patrickxb/fgosqlite/) fork.
-This binding implements the "exp/sql/driver" interface but leaves dangling statements (see drivert_test).
+This binding implements the "exp/sql/driver" interface.
 
 Open supports flags.
 Conn#Exec handles multiple statements (separated by semicolons) properly.
@@ -15,7 +15,7 @@ Stmt#Scan uses native sqlite3_column_x methods.
 Stmt#NamedScan is added. It's compliant with [go-dbi](https://github.com/thomaslee/go-dbi/).
 Stmt#ScanByIndex/ScanByName are added to test NULL value.
 
-Currently, the weak point of the binding is the *Scan methods:
+Currently, the weak point of the binding is the *Scan* methods:
 The original implementation is using this strategy:
  - convert the stored value to a []byte by calling sqlite3_column_bytes,
  - convert the bytes to the desired Go type with correct feedback in case of illegal conversion,
@@ -23,9 +23,7 @@ The original implementation is using this strategy:
 Using the native sqlite3_column_x implies:
  - optimal conversion from the storage type to Go type (when they match),
  - loosy conversion when types mismatch (select cast('M' as int); --> 0),
- - NULL value cannot be returned, default value (0, false, "") is returned instead.
-
-Maybe we should let the caller do the conversion.
+ - NULL value can be returned only for **type, otherwise a default value (0, false, "") is returned.
 
 Misc:
 Conn#Exists
@@ -42,7 +40,7 @@ Conn#EnableLoadExtension/LoadExtension
 Conn#IntegrityCheck
 
 Stmt#ExecInsert/ExecUpdate
-Stmt#BindParameterCount/BindParameterIndex/BindParameterName
+Stmt#BindParameterCount/BindParameterIndex(name)/BindParameterName(index)
 Stmt#ClearBindings
 Stmt#ColumnCount/ColumnNames/ColumnIndex(name)/ColumnName(index)/ColumnType(index)
 Stmt#ReadOnly

function.go

@@ -326,16 +326,12 @@ func (c *Context) Value(i int) (value interface{}) {
 	return
 }
 
-type ScalarFunction func(ctx *Context, nArg int)
+type FuncOrStep func(ctx *Context, nArg int)
 type FinalFunction func(ctx *Context)
 type DestroyFunctionData func(pApp interface{})
 
-/*
-  void (*xStep)(sqlite3_context*,int,sqlite3_value**),
-*/
-
 type sqliteFunction struct {
-	funcOrStep ScalarFunction
+	funcOrStep FuncOrStep
 	final      FinalFunction
 	d          DestroyFunctionData
 	pApp       interface{}
@@ -373,15 +369,26 @@ func goXFunc(scp, udfp, ctxp unsafe.Pointer, argc int, argv unsafe.Pointer) {
 
 //export goXStep
 func goXStep(scp, udfp unsafe.Pointer, argc int, argv unsafe.Pointer) {
-	//udf := (*sqliteFunction)(udfp)
-	//c := nil // FIXME
+	udf := (*sqliteFunction)(udfp)
+	var c *Context
+	c = (*Context)(C.sqlite3_aggregate_context((*C.sqlite3_context)(scp), C.int(unsafe.Sizeof(c))))
+	if c != nil {
+		c.sc = (*C.sqlite3_context)(scp)
+
+		c.argv = (**C.sqlite3_value)(argv)
+		udf.funcOrStep(c, argc)
+		c.argv = nil
+	}
 }
 
 //export goXFinal
 func goXFinal(scp, udfp unsafe.Pointer) {
-	//udf := (*sqliteFunction)(udfp)
-	//c := nil // FIXME (*C.sqlite3_context)(scp)
-	//udf.final(c)
+	udf := (*sqliteFunction)(udfp)
+	c := (*Context)(C.sqlite3_aggregate_context((*C.sqlite3_context)(scp), 0))
+	if c != nil {
+		//c.sc = (*C.sqlite3_context)(scp)
+		udf.final(c)
+	}
 }
 
 //export goXDestroy
@@ -395,7 +402,7 @@ func goXDestroy(pApp unsafe.Pointer) {
 // Create or redefine SQL functions
 // TODO Make possible to specify the preferred encoding
 // Calls http://sqlite.org/c3ref/create_function.html
-func (c *Conn) CreateScalarFunction(functionName string, nArg int, pApp interface{}, f ScalarFunction, d DestroyFunctionData) error {
+func (c *Conn) CreateScalarFunction(functionName string, nArg int, pApp interface{}, f FuncOrStep, d DestroyFunctionData) error {
 	fname := C.CString(functionName)
 	defer C.free(unsafe.Pointer(fname))
 	if f == nil {
@@ -413,16 +420,11 @@ func (c *Conn) CreateScalarFunction(functionName string, nArg int, pApp interfac
 	return c.error(C.goSqlite3CreateScalarFunction(c.db, fname, C.int(nArg), C.SQLITE_UTF8, unsafe.Pointer(udf)))
 }
 
-// Calls http://sqlite.org/c3ref/aggregate_context.html
-func (c *Context) AggregateContext(nBytes int) interface{} {
-	return C.sqlite3_aggregate_context(c.sc, C.int(nBytes))
-}
-
 // Create or redefine SQL functions
 // TODO Make possible to specify the preferred encoding
 // Calls http://sqlite.org/c3ref/create_function.html
 func (c *Conn) CreateAggregateFunction(functionName string, nArg int, pApp interface{},
-	step ScalarFunction, final FinalFunction, d DestroyFunctionData) error {
+	step FuncOrStep, final FinalFunction, d DestroyFunctionData) error {
 	fname := C.CString(functionName)
 	defer C.free(unsafe.Pointer(fname))
 	if step == nil {

function_test.go

@@ -88,7 +88,7 @@ func TestRegexpFunction(t *testing.T) {
 	}
 }
 
-/*
+
 func sumStep(ctx *Context, nArg int) {
 	nt := ctx.NumericType(0)
 	if nt == Integer || nt == Float {
@@ -122,7 +122,6 @@ func TestSumFunction(t *testing.T) {
 		t.Errorf("Expected %d but got %d", 4, i)
 	}
 }
-*/
 
 func randomFill(db *Conn, n int) {
 	db.Exec("DROP TABLE IF EXISTS test")