datastore: variadic Get, Put, Exists, Delete.

service/datastore/types.go

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 //go:generate stringer -type=Toggle
 
 package datastore
 
 // GeoPoint represents a location as latitude/longitude in degrees.
 //
@@ skipping 29 matching lines @@
 // Toggle is a tri-state boolean (Auto/True/False), which allows structs
 // to control boolean flags for metadata in a non-ambiguous way.
 type Toggle byte
 
 // These are the allowed values for Toggle. Any other values are invalid.
 const (
         Auto Toggle = iota
         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")
+        }
+}