While porting LLDB over to StringRef, I am continuously running into difficulties caused by the fact that StringRef cannot be constructed from nullptr. So I wanted to see peoples’ thoughts on removing this restriction from StringRef. To be clear, I’m only using LLDB as a motivating example, but I’m not requesting that it be done because LLDB is some kind of special case. If it is to be done it should be on its own merits. That said, here is some context:
LLDB has a lot of functions that look like this:
void foo(const char *, Bar, const char *).
I’m trying to port these to functions that look like this:
void foo(StringRef, Bar, StringRef).
Often times the parameters are string literals or char arrays, but equally often they are another const char* that got passed into the calling function, or a return value from a CRT function like strstr(), or many other possible sources. This latter category presents a problem for porting code to StringRef, because if I simply change the function signature and fix up compile errors, I will probably have introduced a bug because hundreds of callers will now be implicitly converting from const char* to StringRef, leaving open the possibility that one of those was null.
To work around this, I’ve started doing the following every time I port a function:
void foo(const char , Bar, const char) = delete;
This is pretty hackish, but it gets the job done. At least the compiler warns me and forces me to go inspect every callsite where there’s an implicit conversion. Unfortunately it also makes for extremely verbose code. Now instead of:
foo(“bar”, baz, “buzz”)
I have to write
foo(StringRef(“bar”), baz, StringRef(“buzz”))
even for string literals and char arrays, which will obviously never be null! If StringRef would handle a null argument gracefully, it would make my life much easier.
With that out of the way, here are some reasons I can see to allow StringRef accept null to its constructor which are independent of LLDB and stand on their own merit.
std::string_view<> can be constructed with null. I don’t know when we will be able to use std::string_view<>, but there’s a chance that at some point in the future we may wish to remove StringRef in favor of string_view. That day isn’t soon, but in any case, it will be easier if our assumptions are the same.
[nullptr, nullptr+0) is a valid range. Why shouldn’t we be able to construct a StringRef from an otherwise perfectly valid range?
StringRef() can already be constructed from nullptr (!) Surprised? That’s what happens when you invoke the default constructor. It happily initializes the internal Data with null. So why not allow the same behavior when invoking the const char * constructor?