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? -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20190429/6d3f6c7c/attachment.html>
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?
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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Ah, that makes sense. Thanks! On Mon, Apr 29, 2019 at 11:43 PM Craig Topper <craig.topper at gmail.com> wrote:> 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? >> >> _______________________________________________ >> LLVM Developers mailing list >> llvm-dev at lists.llvm.org >> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev >> >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20190429/afa551f4/attachment.html>