[ADT] Add llvm::StringLiteral.

StringLiteral is a wrapper around a string literal useful for
replacing global tables of char arrays with global tables of
StringRefs that can initialized in a constexpr context, avoiding
the invocation of a global constructor.

Differential Revision: https://reviews.llvm.org/D27686

llvm-svn: 289551
This commit is contained in:
Zachary Turner 2016-12-13 17:03:49 +00:00
parent 09d5daab49
commit bc48d20ef7
2 changed files with 28 additions and 5 deletions

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@ -84,11 +84,8 @@ namespace llvm {
/// Construct a string ref from a pointer and length.
LLVM_ATTRIBUTE_ALWAYS_INLINE
/*implicit*/ StringRef(const char *data, size_t length)
: Data(data), Length(length) {
assert((data || length == 0) &&
"StringRef cannot be built from a NULL argument with non-null length");
}
/*implicit*/ constexpr StringRef(const char *data, size_t length)
: Data(data), Length(length) {}
/// Construct a string ref from an std::string.
LLVM_ATTRIBUTE_ALWAYS_INLINE
@ -839,6 +836,26 @@ namespace llvm {
/// @}
};
/// A wrapper around a string literal that serves as a proxy for constructing
/// global tables of StringRefs with the length computed at compile time.
/// Using this class with a non-literal char array is considered undefined
/// behavior. To prevent this, it is recommended that StringLiteral *only*
/// be used in a constexpr context, as such:
///
/// constexpr StringLiteral S("test");
///
/// Note: There is a subtle behavioral difference in the constructor of
/// StringRef and StringLiteral, as illustrated below:
///
/// constexpr StringLiteral S("a\0b"); // S.size() == 3
/// StringRef S("a\0b"); // S.size() == 1
///
class StringLiteral : public StringRef {
public:
template <size_t N>
constexpr StringLiteral(const char (&Str)[N]) : StringRef(Str, N - 1) {}
};
/// @name StringRef Comparison Operators
/// @{

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@ -1002,4 +1002,10 @@ TEST(StringRefTest, DropWhileUntil) {
EXPECT_EQ("", Taken);
}
TEST(StringRefTest, StringLiteral) {
constexpr StringLiteral Strings[] = {"Foo", "Bar"};
EXPECT_EQ(StringRef("Foo"), Strings[0]);
EXPECT_EQ(StringRef("Bar"), Strings[1]);
}
} // end anonymous namespace