diff options
Diffstat (limited to 'absl/strings/str_cat.h')
| -rw-r--r-- | absl/strings/str_cat.h | 162 |
1 files changed, 112 insertions, 50 deletions
diff --git a/absl/strings/str_cat.h b/absl/strings/str_cat.h index 6ee88f14..fcd48c4e 100644 --- a/absl/strings/str_cat.h +++ b/absl/strings/str_cat.h @@ -48,19 +48,58 @@ // `StrCat()` or `StrAppend()`. You may specify a minimum hex field width using // a `PadSpec` enum. // +// User-defined types can be formatted with the `AbslStringify()` customization +// point. The API relies on detecting an overload in the user-defined type's +// namespace of a free (non-member) `AbslStringify()` function as a definition +// (typically declared as a friend and implemented in-line. +// with the following signature: +// +// class MyClass { ... }; +// +// template <typename Sink> +// void AbslStringify(Sink& sink, const MyClass& value); +// +// An `AbslStringify()` overload for a type should only be declared in the same +// file and namespace as said type. +// +// Note that `AbslStringify()` also supports use with `absl::StrFormat()` and +// `absl::Substitute()`. +// +// Example: +// +// struct Point { +// // To add formatting support to `Point`, we simply need to add a free +// // (non-member) function `AbslStringify()`. This method specifies how +// // Point should be printed when absl::StrCat() is called on it. You can add +// // such a free function using a friend declaration within the body of the +// // class. The sink parameter is a templated type to avoid requiring +// // dependencies. +// template <typename Sink> friend void AbslStringify(Sink& +// sink, const Point& p) { +// absl::Format(&sink, "(%v, %v)", p.x, p.y); +// } +// +// int x; +// int y; +// }; // ----------------------------------------------------------------------------- #ifndef ABSL_STRINGS_STR_CAT_H_ #define ABSL_STRINGS_STR_CAT_H_ +#include <algorithm> #include <array> #include <cstdint> +#include <cstring> #include <string> #include <type_traits> #include <utility> #include <vector> +#include "absl/base/attributes.h" #include "absl/base/port.h" +#include "absl/strings/internal/has_absl_stringify.h" +#include "absl/strings/internal/stringify_sink.h" #include "absl/strings/numbers.h" #include "absl/strings/string_view.h" @@ -77,32 +116,6 @@ struct AlphaNumBuffer { size_t size; }; -class StringifySink { - public: - void Append(size_t count, char ch); - - void Append(string_view v); - - bool PutPaddedString(string_view v, int width, int precision, bool left); - - // Support `absl::Format(&sink, format, args...)`. - friend void AbslFormatFlush(StringifySink* sink, absl::string_view v) { - sink->Append(v); - } - - template <typename T> - friend string_view ExtractStringification(StringifySink& sink, const T& v); - - private: - std::string buffer_; -}; - -template <typename T> -string_view ExtractStringification(StringifySink& sink, const T& v) { - AbslStringify(sink, v); - return sink.buffer_; -} - } // namespace strings_internal // Enum that specifies the number of significant digits to return in a `Hex` or @@ -191,6 +204,27 @@ struct Hex { explicit Hex(Pointee* v, PadSpec spec = absl::kNoPad) : Hex(spec, reinterpret_cast<uintptr_t>(v)) {} + template <typename S> + friend void AbslStringify(S& sink, Hex hex) { + static_assert( + numbers_internal::kFastToBufferSize >= 32, + "This function only works when output buffer >= 32 bytes long"); + char buffer[numbers_internal::kFastToBufferSize]; + char* const end = &buffer[numbers_internal::kFastToBufferSize]; + auto real_width = + absl::numbers_internal::FastHexToBufferZeroPad16(hex.value, end - 16); + if (real_width >= hex.width) { + sink.Append(absl::string_view(end - real_width, real_width)); + } else { + // Pad first 16 chars because FastHexToBufferZeroPad16 pads only to 16 and + // max pad width can be up to 20. + std::memset(end - 32, hex.fill, 16); + // Patch up everything else up to the real_width. + std::memset(end - real_width - 16, hex.fill, 16); + sink.Append(absl::string_view(end - hex.width, hex.width)); + } + } + private: Hex(PadSpec spec, uint64_t v) : value(v), @@ -225,6 +259,38 @@ struct Dec { : spec - absl::kZeroPad2 + 2), fill(spec >= absl::kSpacePad2 ? ' ' : '0'), neg(v < 0) {} + + template <typename S> + friend void AbslStringify(S& sink, Dec dec) { + assert(dec.width <= numbers_internal::kFastToBufferSize); + char buffer[numbers_internal::kFastToBufferSize]; + char* const end = &buffer[numbers_internal::kFastToBufferSize]; + char* const minfill = end - dec.width; + char* writer = end; + uint64_t val = dec.value; + while (val > 9) { + *--writer = '0' + (val % 10); + val /= 10; + } + *--writer = '0' + static_cast<char>(val); + if (dec.neg) *--writer = '-'; + + ptrdiff_t fillers = writer - minfill; + if (fillers > 0) { + // Tricky: if the fill character is ' ', then it's <fill><+/-><digits> + // But...: if the fill character is '0', then it's <+/-><fill><digits> + bool add_sign_again = false; + if (dec.neg && dec.fill == '0') { // If filling with '0', + ++writer; // ignore the sign we just added + add_sign_again = true; // and re-add the sign later. + } + writer -= fillers; + std::fill_n(writer, fillers, dec.fill); + if (add_sign_again) *--writer = '-'; + } + + sink.Append(absl::string_view(writer, static_cast<size_t>(end - writer))); + } }; // ----------------------------------------------------------------------------- @@ -232,17 +298,10 @@ struct Dec { // ----------------------------------------------------------------------------- // // The `AlphaNum` class acts as the main parameter type for `StrCat()` and -// `StrAppend()`, providing efficient conversion of numeric, boolean, and -// hexadecimal values (through the `Hex` type) into strings. - -template <typename T, typename = void> -struct HasAbslStringify : std::false_type {}; - -template <typename T> -struct HasAbslStringify<T, std::enable_if_t<std::is_void<decltype(AbslStringify( - std::declval<strings_internal::StringifySink&>(), - std::declval<const T&>()))>::value>> - : std::true_type {}; +// `StrAppend()`, providing efficient conversion of numeric, boolean, decimal, +// and hexadecimal values (through the `Dec` and `Hex` types) into strings. +// `AlphaNum` should only be used as a function parameter. Do not instantiate +// `AlphaNum` directly as a stack variable. class AlphaNum { public: @@ -279,28 +338,30 @@ class AlphaNum { AlphaNum(double f) // NOLINT(runtime/explicit) : piece_(digits_, numbers_internal::SixDigitsToBuffer(f, digits_)) {} - AlphaNum(Hex hex); // NOLINT(runtime/explicit) - AlphaNum(Dec dec); // NOLINT(runtime/explicit) - template <size_t size> AlphaNum( // NOLINT(runtime/explicit) - const strings_internal::AlphaNumBuffer<size>& buf) + const strings_internal::AlphaNumBuffer<size>& buf + ABSL_ATTRIBUTE_LIFETIME_BOUND) : piece_(&buf.data[0], buf.size) {} - AlphaNum(const char* c_str) // NOLINT(runtime/explicit) - : piece_(NullSafeStringView(c_str)) {} // NOLINT(runtime/explicit) - AlphaNum(absl::string_view pc) : piece_(pc) {} // NOLINT(runtime/explicit) + AlphaNum(const char* c_str // NOLINT(runtime/explicit) + ABSL_ATTRIBUTE_LIFETIME_BOUND) + : piece_(NullSafeStringView(c_str)) {} + AlphaNum(absl::string_view pc // NOLINT(runtime/explicit) + ABSL_ATTRIBUTE_LIFETIME_BOUND) + : piece_(pc) {} template <typename T, typename = typename std::enable_if< - HasAbslStringify<T>::value>::type> - AlphaNum( // NOLINT(runtime/explicit) - const T& v, // NOLINT(runtime/explicit) - strings_internal::StringifySink&& sink = {}) // NOLINT(runtime/explicit) + strings_internal::HasAbslStringify<T>::value>::type> + AlphaNum( // NOLINT(runtime/explicit) + const T& v ABSL_ATTRIBUTE_LIFETIME_BOUND, + strings_internal::StringifySink&& sink ABSL_ATTRIBUTE_LIFETIME_BOUND = {}) : piece_(strings_internal::ExtractStringification(sink, v)) {} template <typename Allocator> AlphaNum( // NOLINT(runtime/explicit) - const std::basic_string<char, std::char_traits<char>, Allocator>& str) + const std::basic_string<char, std::char_traits<char>, Allocator>& str + ABSL_ATTRIBUTE_LIFETIME_BOUND) : piece_(str) {} // Use string literals ":" instead of character literals ':'. @@ -317,7 +378,8 @@ class AlphaNum { // This overload matches only scoped enums. template <typename T, typename = typename std::enable_if< - std::is_enum<T>{} && !std::is_convertible<T, int>{}>::type> + std::is_enum<T>{} && !std::is_convertible<T, int>{} && + !strings_internal::HasAbslStringify<T>::value>::type> AlphaNum(T e) // NOLINT(runtime/explicit) : AlphaNum(static_cast<typename std::underlying_type<T>::type>(e)) {} |