[PATCH] D25639: Add ctor for string literal to StringRef, and make explicit the conversion from const char *

Mehdi Amini via llvm-commits llvm-commits at lists.llvm.org
Mon Oct 17 12:38:01 PDT 2016

> On Oct 17, 2016, at 10:12 AM, David Blaikie <dblaikie at gmail.com> wrote:
> (for my money the readability loss of adding StringRef(...) all over the place doesn't seem quite worth it, but I'm not going to stand in the way of the change or anything.)

The balance is between the readability, and the “error prone” current behavior.

For example we introduced all these redundant .c_str() in the past: https://reviews.llvm.org/D25667 <https://reviews.llvm.org/D25667>
Ideally we shouldn’t have much explicit calls to StringRef, if all the APIs are converted to work with StringRef most of the time. 

> Are these changes necessarily joined - or is the explicitness of the StringRef(...) ctor independent of the addition of the template?

It is not independent: the template is never selected if the other constructor is not made explicit.

> Do we need to worry about the recursive strlen in the template ctor? Or is it clear that even in a non-constexpr context the compilers we care about produce reasonable performance?

Can you clarify what you mean by "non-constexpr context” here?
The recursive template is not intended to be used with anything else than literal, I am not expecting this to generate any code ever (if it does, it is not intended).


> On Mon, Oct 17, 2016 at 12:57 AM Manuel Klimek via llvm-commits <llvm-commits at lists.llvm.org <mailto:llvm-commits at lists.llvm.org>> wrote:
> klimek added a comment.
> In https://reviews.llvm.org/D25639#571344 <https://reviews.llvm.org/D25639#571344>, @zturner wrote:
> > The only thing I'm not crazy about here is that the clang tidy check seems to blindly replace all calls to `s.c_str()` with `llvm::StringRef(s.c_str())`.  Is there any way to make it attempt to replace it with just `s` first, and only if that fails do you then try `llvm::StringRef(s.c_str())`?
> Shouldn't it be relatively straight forward to discover whether the expression is convertible to StringRef without the .c_str() call from an AST matcher?
> https://reviews.llvm.org/D25639 <https://reviews.llvm.org/D25639>
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