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

[Pete Cooper via llvm-commits]

Very useful! I know a few places I would have liked to have had these.

LGTM.

Pete

Sent from my iPhone

> On Jul 23, 2016, at 1:40 AM, Chandler Carruth via llvm-commits <llvm-commits at lists.llvm.org> wrote:
> 
> 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
> 
> 
> <D22723.65218.patch>
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