[llvm-dev] How does Twine work?

[Craig Topper via llvm-dev]

I believe StringRef + const char* is overloaded at the bottom of Twine.h.
And without those overloads it might try to implicitly convert both
StringRef and const char* to Twine and then add them since StringRef +
const char * wouldn't otherwise be defined.

  inline Twine operator+(const Twine &LHS, const Twine &RHS) {
    return LHS.concat(RHS);
  }

  /// Additional overload to guarantee simplified codegen; this is
equivalent to
  /// concat().

  inline Twine operator+(const char *LHS, const StringRef &RHS) {
    return Twine(LHS, RHS);
  }

  /// Additional overload to guarantee simplified codegen; this is
equivalent to
  /// concat().

  inline Twine operator+(const StringRef &LHS, const char *RHS) {
    return Twine(LHS, RHS);
  }



~Craig


On Mon, Apr 29, 2019 at 3:18 PM Russell Wallace via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> I'm looking at the documentation on Twine at
> http://llvm.org/docs/ProgrammersManual.html#llvm-adt-twine-h and it gives
> example code:
>
> void foo(const Twine &T);
> ...
> StringRef X = ...
> unsigned i = ...
> foo(X + "." + Twine(i));
>
> How exactly does that last line work? Since addition is left associative,
> I would expect it to be parsed as (X + ".") ... so it's trying to add a
> StringRef and a const char* before Twine can come into the picture at all?
>
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