Avoid utf8CString when when owned storage is not required

Sources/FoundationInternationalization/ICU/ICU+CaseMap.swift

@@ -58,17 +58,23 @@ extension ICU {
         }
 
         func lowercase(_ s: String) -> String? {
-            s.utf8CString.withUnsafeBufferPointer { srcBuf in
-                _withResizingCharBuffer { destBuf, destSize, status in
-                    ucasemap_utf8ToLower(casemap, destBuf, destSize, srcBuf.baseAddress!, Int32(srcBuf.count), &status)
+            var s = s
+            return s.withUTF8 { srcBuf in
+                srcBuf.withMemoryRebound(to: CChar.self) { srcBuf in
+                    _withResizingCharBuffer { destBuf, destSize, status in
+                        ucasemap_utf8ToLower(casemap, destBuf, destSize, srcBuf.baseAddress!, Int32(srcBuf.count), &status)
+                    }
                 }
             }
         }
 
         func uppercase(_ s: String) -> String? {
-            s.utf8CString.withUnsafeBufferPointer { srcBuf in
-                _withResizingCharBuffer { destBuf, destSize, status in
-                    ucasemap_utf8ToUpper(casemap, destBuf, destSize, srcBuf.baseAddress!, Int32(srcBuf.count), &status)
+            var s = s
+            return s.withUTF8 { srcBuf in
+                srcBuf.withMemoryRebound(to: CChar.self) { srcBuf in
+                    _withResizingCharBuffer { destBuf, destSize, status in
+                        ucasemap_utf8ToUpper(casemap, destBuf, destSize, srcBuf.baseAddress!, Int32(srcBuf.count), &status)
+                    }
                 }
             }
         }
@@ -77,9 +83,11 @@ extension ICU {
             lock.withLock { _ in
                 var s = s
                 return s.withUTF8 { srcBuf in
-                    srcBuf.withMemoryRebound(to: CChar.self) { buffer in
-                        _withResizingCharBuffer { destBuf, destSize, status in
-                            ucasemap_utf8ToTitle(casemap, destBuf, destSize, buffer.baseAddress!, Int32(buffer.count), &status)
+                    srcBuf.withMemoryRebound(to: CChar.self) { srcBuf in
+                        srcBuf.withMemoryRebound(to: CChar.self) { buffer in
+                            _withResizingCharBuffer { destBuf, destSize, status in
+                                ucasemap_utf8ToTitle(casemap, destBuf, destSize, buffer.baseAddress!, Int32(buffer.count), &status)
+                            }
                         }
                     }
                 }
@@ -89,18 +97,24 @@ extension ICU {
         func titlecase(_ s: String) -> String? {
             // `ucasemap_utf8ToTitle` isn't thread-safe
             lock.withLock { _ in
-                s.utf8CString.withUnsafeBufferPointer { srcBuf in
-                    _withResizingCharBuffer { destBuf, destSize, status in
-                        ucasemap_utf8ToTitle(casemap, destBuf, destSize, srcBuf.baseAddress!, Int32(srcBuf.count), &status)
+                var s = s
+                return s.withUTF8 { srcBuf in
+                    srcBuf.withMemoryRebound(to: CChar.self) { srcBuf in
+                        _withResizingCharBuffer { destBuf, destSize, status in
+                            ucasemap_utf8ToTitle(casemap, destBuf, destSize, srcBuf.baseAddress!, Int32(srcBuf.count), &status)
+                        }
                     }
                 }
             }
         }
 
         func foldcase(_ s: String) -> String? {
-            s.utf8CString.withUnsafeBufferPointer { srcBuf in
-                _withResizingCharBuffer { destBuf, destSize, status in
-                    ucasemap_utf8FoldCase(casemap, destBuf, destSize, srcBuf.baseAddress!, Int32(srcBuf.count), &status)
+            var s = s
+            return s.withUTF8 { srcBuf in
+                srcBuf.withMemoryRebound(to: CChar.self) { srcBuf in
+                    _withResizingCharBuffer { destBuf, destSize, status in
+                        ucasemap_utf8FoldCase(casemap, destBuf, destSize, srcBuf.baseAddress!, Int32(srcBuf.count), &status)
+                    }
                 }
             }
         }

Sources/FoundationInternationalization/ICU/ICU+Foundation.swift

@@ -158,9 +158,7 @@ internal func _withFixedCharBuffer(size: Int32 = ULOC_FULLNAME_CAPACITY + ULOC_K
 /// Use this function for ICU API which takes a C string and returns a C string. ICU may choose to return the original pointer, making the usual pattern of simply calling `String(cString: result)` use deallocated memory.
 /// See also: rdar://104711456 and rdar://104710940
 internal func _withStringAsCString(_ input: String, _ body: (UnsafePointer<CChar>) -> UnsafePointer<CChar>?) -> String? {
-    return input.utf8CString.withUnsafeBufferPointer { buffer -> String? in
-        // Intentional force unwrap
-        let base = buffer.baseAddress!
+    return input.withCString { base -> String? in
         guard let result = body(base) else {
             return nil
         }

Sources/FoundationInternationalization/String/String+Comparison_ICU.swift

@@ -20,8 +20,8 @@ internal func compareStringsWithLocale(_ string1: Substring, _ string2: Substrin
     let localeIdentifier = locale.identifier
     var status = U_ZERO_ERROR
 
-    let collator = localeIdentifier.utf8CString.withUnsafeBufferPointer({ buffer in
-        ucol_open(buffer.baseAddress, &status)
+    let collator = localeIdentifier.withCString({ ptr in
+        ucol_open(ptr, &status)
     })
 
     defer {

Tests/FoundationEssentialsTests/DataTests.swift

@@ -99,11 +99,9 @@ private final class DataTests {
     // String of course has its own way to get data, but this way tests our own data struct
     func dataFrom(_ string : String) -> Data {
         // Create a Data out of those bytes
-        return string.utf8CString.withUnsafeBufferPointer { (ptr) in
-            ptr.baseAddress!.withMemoryRebound(to: UInt8.self, capacity: ptr.count) {
-                // Subtract 1 so we don't get the null terminator byte. This matches NSString behavior.
-                return Data(bytes: $0, count: ptr.count - 1)
-            }
+        var string = string
+        return string.withUTF8 { (ptr) in
+            return Data(buffer: ptr)
         }
     }