Add StringRef::{slice, split}, two convenient string operations which are simple

and efficient on a StringRef.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@77117 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/StringRef.h

@@ -10,6 +10,7 @@
 #ifndef LLVM_ADT_STRINGREF_H
 #define LLVM_ADT_STRINGREF_H
 
+#include <algorithm>
 #include <cassert>
 #include <cstring>
 #include <string>
@@ -120,11 +121,11 @@ namespace llvm {
     /// @name Utility Functions
     /// @{
 
-    /// substr - Return a reference to a substring of this object.
+    /// substr - Return a reference to the substring from [Start, Start + N).
     ///
     /// \param Start - The index of the starting character in the substring; if
-    /// the index is greater than the length of the string then the empty
-    /// substring will be returned.
+    /// the index is npos or greater than the length of the string then the
+    /// empty substring will be returned.
     ///
     /// \param N - The number of characters to included in the substring. If N
     /// exceeds the number of characters remaining in the string, the string
@@ -134,6 +135,40 @@ namespace llvm {
       return StringRef(Data + Start, std::min(N, Length - Start));
     }
 
+    /// slice - Return a reference to the substring from [Start, End).
+    ///
+    /// \param Start - The index of the starting character in the substring; if
+    /// the index is npos or greater than the length of the string then the
+    /// empty substring will be returned.
+    ///
+    /// \param End - The index following the last character to include in the
+    /// substring. If this is npos, or less than \arg Start, or exceeds the
+    /// number of characters remaining in the string, the string suffix
+    /// (starting with \arg Start) will be returned.
+    StringRef slice(size_t Start, size_t End) const {
+      Start = std::min(Start, Length);
+      End = std::min(std::max(Start, End), Length);
+      return StringRef(Data + Start, End - Start);
+    }
+
+    /// split - Split into two substrings around the first occurence of a
+    /// separator character.
+    ///
+    /// If \arg Separator is in the string, then the result is a pair (LHS, RHS)
+    /// such that (*this == LHS + Separator + RHS) is true and RHS is
+    /// maximal. If \arg Separator is not in the string, then the result is a
+    /// pair (LHS, RHS) where (*this == LHS) and (RHS == "").
+    ///
+    /// \param Separator - The character to split on.
+    /// \return - The split substrings.
+    std::pair<StringRef, StringRef> split(char Separator) const {
+      iterator it = std::find(begin(), end(), Separator);
+      if (it == end())
+        return std::make_pair(*this, StringRef());
+      return std::make_pair(StringRef(begin(), it - begin()),
+                            StringRef(it + 1, end() - (it + 1)));
+    }
+
     /// startswith - Check if this string starts with the given \arg Prefix.
     bool startswith(const StringRef &Prefix) const { 
       return substr(0, Prefix.Length).equals(Prefix);

unittests/ADT/StringRefTest.cpp

@@ -64,6 +64,21 @@ TEST(StringRefTest, Utilities) {
   EXPECT_TRUE(Str.substr(0, 100) == "hello");
   EXPECT_TRUE(Str.substr(4, 10) == "o");
 
+  EXPECT_TRUE(Str.slice(2, 3) == "l");
+  EXPECT_TRUE(Str.slice(1, 4) == "ell");
+  EXPECT_TRUE(Str.slice(2, 100) == "llo");
+  EXPECT_TRUE(Str.slice(2, 1) == "");
+  EXPECT_TRUE(Str.slice(10, 20) == "");
+
+  EXPECT_TRUE(Str.split('X') == std::make_pair(StringRef("hello"), 
+                                               StringRef("")));
+  EXPECT_TRUE(Str.split('e') == std::make_pair(StringRef("h"), 
+                                               StringRef("llo")));
+  EXPECT_TRUE(Str.split('h') == std::make_pair(StringRef(""), 
+                                               StringRef("ello")));
+  EXPECT_TRUE(Str.split('o') == std::make_pair(StringRef("hell"), 
+                                               StringRef("")));
+
   EXPECT_TRUE(Str.startswith("he"));
   EXPECT_FALSE(Str.startswith("helloworld"));
   EXPECT_FALSE(Str.startswith("hi"));