[PATCH] D22723: [ADT] Add 'consume_front' and 'consume_back' methods to StringRef which are very handy when parsing text.

[Chandler Carruth via llvm-commits]

chandlerc created this revision.
chandlerc added a subscriber: llvm-commits.
Herald added a subscriber: mcrosier.

They are essentially a combination of startswith and a self-modifying
drop_front, or endswith and drop_back respectively.

https://reviews.llvm.org/D22723

Files:
  include/llvm/ADT/StringRef.h
  unittests/ADT/StringRefTest.cpp

Index: unittests/ADT/StringRefTest.cpp
===================================================================
--- unittests/ADT/StringRefTest.cpp
+++ unittests/ADT/StringRefTest.cpp
@@ -322,6 +322,21 @@
   EXPECT_FALSE(Str.startswith_lower("hi"));
 }
 
+TEST(StringRefTest, ConsumeFront) {
+  StringRef Str("hello");
+  EXPECT_TRUE(Str.consume_front(""));
+  EXPECT_EQ("hello", Str);
+  EXPECT_TRUE(Str.consume_front("he"));
+  EXPECT_EQ("llo", Str);
+  EXPECT_FALSE(Str.consume_front("lloworld"));
+  EXPECT_EQ("llo", Str);
+  EXPECT_FALSE(Str.consume_front("lol"));
+  EXPECT_EQ("llo", Str);
+  EXPECT_TRUE(Str.consume_front("llo"));
+  EXPECT_EQ("", Str);
+  EXPECT_FALSE(Str.consume_front("o"));
+}
+
 TEST(StringRefTest, EndsWith) {
   StringRef Str("hello");
   EXPECT_TRUE(Str.endswith(""));
@@ -341,6 +356,21 @@
   EXPECT_FALSE(Str.endswith_lower("hi"));
 }
 
+TEST(StringRefTest, ConsumeBack) {
+  StringRef Str("hello");
+  EXPECT_TRUE(Str.consume_back(""));
+  EXPECT_EQ("hello", Str);
+  EXPECT_TRUE(Str.consume_back("lo"));
+  EXPECT_EQ("hel", Str);
+  EXPECT_FALSE(Str.consume_back("helhel"));
+  EXPECT_EQ("hel", Str);
+  EXPECT_FALSE(Str.consume_back("hle"));
+  EXPECT_EQ("hel", Str);
+  EXPECT_TRUE(Str.consume_back("hel"));
+  EXPECT_EQ("", Str);
+  EXPECT_FALSE(Str.consume_back("h"));
+}
+
 TEST(StringRefTest, Find) {
   StringRef Str("hello");
   EXPECT_EQ(2U, Str.find('l'));
Index: include/llvm/ADT/StringRef.h
===================================================================
--- include/llvm/ADT/StringRef.h
+++ include/llvm/ADT/StringRef.h
@@ -446,6 +446,28 @@
       return substr(0, size()-N);
     }
 
+    /// Returns true if this StringRef has the given prefix and removes that
+    /// prefix.
+    LLVM_ATTRIBUTE_ALWAYS_INLINE
+    bool consume_front(StringRef Prefix) {
+      if (!startswith(Prefix))
+        return false;
+
+      *this = drop_front(Prefix.size());
+      return true;
+    }
+
+    /// Returns true if this StringRef has the given suffix and removes that
+    /// suffix.
+    LLVM_ATTRIBUTE_ALWAYS_INLINE
+    bool consume_back(StringRef Suffix) {
+      if (!endswith(Suffix))
+        return false;
+
+      *this = drop_back(Suffix.size());
+      return true;
+    }
+
     /// Return a reference to the substring from [Start, End).
     ///
     /// \param Start The index of the starting character in the substring; if


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