datastore: variadic Get, Put, Exists, Delete.

service/datastore/types.go

Index: service/datastore/types.go
diff --git a/service/datastore/types.go b/service/datastore/types.go
index 94780f8408ba1cdb889836df6ca330d24d754559..ffc54a9c763a39c710883750d9cc28e122a58f01 100644
--- a/service/datastore/types.go
+++ b/service/datastore/types.go
@@ -47,3 +47,181 @@ const (
 	On
 	Off
 )
+
+// BoolList is a convenience wrapper for []bool that provides summary methods
+// for working with the list in aggregate.
+type BoolList []bool
+
+// All returns true iff all of the booleans in this list are true.
+func (bl BoolList) All() bool {
+	for _, b := range bl {
+		if !b {
+			return false
+		}
+	}
+	return true
+}
+
+// Any returns true iff any of the booleans in this list are true.
+func (bl BoolList) Any() bool {
+	for _, b := range bl {
+		if b {
+			return true
+		}
+	}
+	return false
+}
+
+// ExistsResult is a 2-dimensional boolean array that represents the existence
+// of entries in the datastore. It is returned by the datastore Exists method.
+// It is designed to accommodate the potentially-nested variadic arguments that
+// can be passed to Exists.
+//
+// The first dimension contains one entry for each Exists input index. If the
+// argument is a single entry, the boolean value at this index will be true if
+// that argument was present in the datastore and false otherwise. If the
+// argument is a slice, it will contain an aggregate value that is true iff no
+// values in that slice were missing from the datastore.
+//
+// The second dimension presents a boolean slice for each input argument. Single
+// arguments will have a slice of size 1 whose value corresponds to the first
+// dimension value for that argument. Slice arguments have a slice of the same
+// size. A given index in the second dimension slice is true iff the element at
+// that index was present.
+type ExistsResult struct {
+	// values is the first dimension aggregate values.
+	values BoolList
+	// slices is the set of second dimension positional values.
+	slices []BoolList
+}
+
+func (r *ExistsResult) init(sizes ...int) {
+	// In order to reduce allocations, we allocate a single continuous boolean
+	// slice and then partition it up into first- and second-dimension slices.
+	//
+	// To determine the size of the continuous slize, count the number of elements
+	// that we'll need:
+	// - Single arguments and slice arguments with size 1 will have their
+	//   second-dimension slice just point to their element in the first-dimension
+	//   slice.
+	// - Slice elements of size >1 will have their second-dimension slice added to
+	//   the end of the continuous slice. Their slice will be carved off in the
+	//   subsequent loop.
+	//
+	// Consequently, we need one element for each argument, plus len(slice)
+	// additional elements for each slice argument of size >1.
+	count := len(sizes) // [0..n)
+	for _, s := range sizes {
+		if s > 1 {
+			count += s
+		}
+	}
+
+	// Allocate our continuous array and partition it into first- and
+	// second-dimension slices.
+	entries := make(BoolList, count)
+	r.values, entries = entries[:len(sizes)], entries[len(sizes):]
+	r.slices = make([]BoolList, len(sizes))
+	for i, s := range sizes {
+		switch {
+		case s <= 0:
+			break
+
+		case s == 1:
+			// Single-entry slice out of "entries".
+			r.slices[i] = r.values[i : i+1]
+
+		default:
+			r.slices[i], entries = entries[:s], entries[s:]
+		}
+	}
+}
+
+func (r *ExistsResult) set(i, j int) { r.slices[i][j] = true }
+
+// updateSlices updates the top-level value for multi-dimensional elements based
+// on their current values.
+func (r *ExistsResult) updateSlices() {
+	for i, s := range r.slices {
+		// Zero-length slices will have a first-dimension true value, since they
+		// have no entries and first-dimension is true when there are no false
+		// entries.
+		r.values[i] = (len(s) == 0 || s.All())
+	}
+}
+
+// All returns true if all of the available boolean slots are true.
+func (r *ExistsResult) All() bool { return r.values.All() }
+
+// Any returns true if any of the boolean slots are true.
+func (r *ExistsResult) Any() bool {
+	// We have to implement our own Any so zero-length slices don't count towards
+	// our result.
+	for i, b := range r.values {
+		if b && len(r.slices[i]) > 0 {
+			return true
+		}
+	}
+	return false
+}
+
+// Get returns the boolean value at the specified index.
+//
+// The one-argument form returns the first-dimension boolean. If i is a slice
+// argument, this will be true iff all of the slice's booleans are true.
+//
+// An optional second argument can be passed to access a specific boolean value
+// in slice i. If the argument at i is a single argument, the only valid index,
+// 0, will be the same as calling the single-argument Get.
+//
+// Passing more than one additional argument will result in a panic.
+func (r *ExistsResult) Get(i int, j ...int) bool {
+	switch len(j) {
+	case 0:
+		return r.values[i]
+	case 1:
+		return r.slices[i][j[0]]
+	default:
+		panic("this method takes one or two arguments")
+	}
+}
+
+// List returns the BoolList for the given argument index.
+//
+// The zero-argument form returns the first-dimension boolean list.
+//
+// An optional argument can be passed to access a specific argument's boolean
+// slice. If the argument at i is a non-slice argument, the list will be a slice
+// of size 1 containing i's first-dimension value.
+//
+// Passing more than one argument will result in a panic.
+func (r *ExistsResult) List(i ...int) BoolList {
+	switch len(i) {
+	case 0:
+		return r.values
+	case 1:
+		return r.slices[i[0]]
+	default:
+		panic("this method takes zero or one arguments")
+	}
+}
+
+// Len returns the number of boolean results available.
+//
+// The zero-argument form returns the first-dimension size, which will equal the
+// total number of arguments passed to Exists.
+//
+// The one-argument form returns the number of booleans in the slice for
+// argument i.
+//
+// Passing more than one argument will result in a panic.
+func (r *ExistsResult) Len(i ...int) int {
+	switch len(i) {
+	case 0:
+		return len(r.values)
+	case 1:
+		return len(r.slices[i[0]])
+	default:
+		panic("this method takes zero or one arguments")
+	}
+}