Delete Span's implicit constructors for char* and char16_t* pointers to avoid accidental construction in cases where a pointer does not point to a zero-terminated string. Use the MakeStringSpan() function instead.
I deleted both the const and non-const char* and char16_t* constructors, in the name of cross-compiler consistency. If we only delete the const char* and char16_t* constructors, for some reason, MSVC complains that `Span<char> s(charArray)` uses a deleted constructor while clang nor gcc permit it. I don't know if this is a compiler bug in MSVC or clang and gcc.
Also, do not permit MakeSpan() for string literals (const char and char16_t arrays) because the Span length would include the zero terminator, which may surprise callers. Use MakeStringSpan() to create a Span whose length that excludes the string literal's zero terminator or use the MakeSpan() overload that accepts a pointer and length and specify the string literal's full length.
The following Span usages are prevented:
Span<const char> span("literal"); // error
Span<char> span(charArray); // error
Span<const char> span;
span = "literal"; // error
span = charArray; // error
MakeSpan("literal"); // error
The following Span usages are still permitted:
assert(MakeStringSpan("literal") == 8); // OK: span length is calculated with strlen() and excludes the zero terminator
MakeStringSpan(charArray); // OK: span length is calculated with strlen() and excludes the zero terminator
MakeSpan(charArray); // OK: span length is the char array size including any zero terminator
MozReview-Commit-ID: Et71CpjsiyI
--HG--
extra : rebase_source : f6f8bdb28726f0f2368fdfdd039fb1d7dcf2914e
extra : source : 0547d8924ffc7713d6cf32cc06eeeaf00e0d69a3
I can't speak for whether the MOZ_SPAN_GCC_CONSTEXPR on operator> is necessary, but I'm going on the assumption that any callers of it must also be in the same bucket of constexpr-ness.
Masatoshi Kimura
Chris Peterson
Henri Sivonen
David Major