Merge pull request #2929 from ultramiraculous/slice-base

SE-0093 - Add public base property to slices

Author: gribozavr

stdlib/public/core/Slice.swift.gyb

@@ -435,6 +435,11 @@ public struct ${Self}<Base : ${BaseRequirements}>
 %     else:
   internal let _base: Base
 %     end
+
+  /// The underlying collection of the slice.
+  public var base: Base {
+    return _base
+  }
 }
 
 %     end

validation-test/stdlib/Slice.swift.gyb

@@ -18,6 +18,32 @@ import StdlibCollectionUnittest
 import SwiftPrivate
 
 
+/// Reference-type collection for testing the `base` property.
+class ReferenceCollection : RandomAccessCollection {
+    typealias Index = Int
+    
+    var startIndex: Int {
+        return 0
+    }
+    
+    var endIndex: Int {
+        return 1
+    }
+
+    subscript(index: Int) -> String {
+        return ""
+    }
+    
+    func index(after i: Int) -> Int {
+        return 1
+    }
+    
+    func index(before i: Int) -> Int {
+        return 0
+    }
+}
+
+
 var SliceTests = TestSuite("Collection")
 
 //===----------------------------------------------------------------------===//
@@ -69,6 +95,14 @@ SliceTests.test("${Slice}/init(base:bounds:)") {
   }
 }
 
+% if RangeReplaceable == False and Mutable == False:
+SliceTests.test("${Slice}/baseProperty") {
+  let referenceCollection = ReferenceCollection()
+  let testSlice = ${Slice}(base: referenceCollection, bounds: 0..<1)
+  expectTrue(testSlice.base === referenceCollection)
+}
+% end
+
 SliceTests.test("${Slice}.{startIndex,endIndex}") {
   for test in subscriptRangeTests {
     let c = ${Collection}(elements: test.collection)