Extract   *ExtractFunc   `parser:"| @@"`
	Trim      *TrimFunc      `parser:"| @@"`
	DateAdd   *DateAddFunc   `parser:"| @@"`
	DateDiff  *DateDiffFunc  `parser:"| @@"`

	// Used during evaluation for aggregation funcs
	aggregate *aggVal
}

// SimpleArgFunc represents functions with simple expression
// arguments.
type SimpleArgFunc struct {

func NewGetObjectReaderFromReader(r io.Reader, oi ObjectInfo, opts ObjectOptions, cleanupFns ...func()) (*GetObjectReader, error) {
	if opts.CheckPrecondFn != nil && opts.CheckPrecondFn(oi) {
		// Call the cleanup funcs
		for i := len(cleanupFns) - 1; i >= 0; i-- {
			cleanupFns[i]()
		}
		return nil, PreConditionFailed{}
	}
	return &GetObjectReader{
		ObjInfo:    oi,
		Reader:     r,
		cleanUpFns: cleanupFns,