diff options
Diffstat (limited to 'absl/strings/str_format.h')
| -rw-r--r-- | absl/strings/str_format.h | 302 |
1 files changed, 289 insertions, 13 deletions
diff --git a/absl/strings/str_format.h b/absl/strings/str_format.h index 2f9b4b27..01465107 100644 --- a/absl/strings/str_format.h +++ b/absl/strings/str_format.h @@ -19,7 +19,7 @@ // // The `str_format` library is a typesafe replacement for the family of // `printf()` string formatting routines within the `<cstdio>` standard library -// header. Like the `printf` family, the `str_format` uses a "format string" to +// header. Like the `printf` family, `str_format` uses a "format string" to // perform argument substitutions based on types. See the `FormatSpec` section // below for format string documentation. // @@ -57,8 +57,7 @@ // arbitrary sink types: // // * A generic `Format()` function to write outputs to arbitrary sink types, -// which must implement a `RawSinkFormat` interface. (See -// `str_format_sink.h` for more information.) +// which must implement a `FormatRawSink` interface. // // * A `FormatUntyped()` function that is similar to `Format()` except it is // loosely typed. `FormatUntyped()` is not a template and does not perform @@ -66,8 +65,7 @@ // boolean from a runtime check. // // In addition, the `str_format` library provides extension points for -// augmenting formatting to new types. These extensions are fully documented -// within the `str_format_extension.h` header file. +// augmenting formatting to new types. See "StrFormat Extensions" below. #ifndef ABSL_STRINGS_STR_FORMAT_H_ #define ABSL_STRINGS_STR_FORMAT_H_ @@ -255,8 +253,8 @@ class FormatCountCapture { // argument, etc. template <typename... Args> -using FormatSpec = - typename str_format_internal::FormatSpecDeductionBarrier<Args...>::type; +using FormatSpec = str_format_internal::FormatSpecTemplate< + str_format_internal::ArgumentToConv<Args>()...>; // ParsedFormat // @@ -283,9 +281,36 @@ using FormatSpec = // } else { // ... error case ... // } + +#if defined(__cpp_nontype_template_parameter_auto) +// If C++17 is available, an 'extended' format is also allowed that can specify +// multiple conversion characters per format argument, using a combination of +// `absl::FormatConversionCharSet` enum values (logically a set union) +// via the `|` operator. (Single character-based arguments are still accepted, +// but cannot be combined). Some common conversions also have predefined enum +// values, such as `absl::FormatConversionCharSet::kIntegral`. +// +// Example: +// // Extended format supports multiple conversion characters per argument, +// // specified via a combination of `FormatConversionCharSet` enums. +// using MyFormat = absl::ParsedFormat<absl::FormatConversionCharSet::d | +// absl::FormatConversionCharSet::x>; +// MyFormat GetFormat(bool use_hex) { +// if (use_hex) return MyFormat("foo %x bar"); +// return MyFormat("foo %d bar"); +// } +// // `format` can be used with any value that supports 'd' and 'x', +// // like `int`. +// auto format = GetFormat(use_hex); +// value = StringF(format, i); +template <auto... Conv> +using ParsedFormat = absl::str_format_internal::ExtendedParsedFormat< + absl::str_format_internal::ToFormatConversionCharSet(Conv)...>; +#else template <char... Conv> using ParsedFormat = str_format_internal::ExtendedParsedFormat< - str_format_internal::ConversionCharToConv(Conv)...>; + absl::str_format_internal::ToFormatConversionCharSet(Conv)...>; +#endif // defined(__cpp_nontype_template_parameter_auto) // StrFormat() // @@ -432,6 +457,16 @@ int SNPrintF(char* output, std::size_t size, const FormatSpec<Args...>& format, // // FormatRawSink is a type erased wrapper around arbitrary sink objects // specifically used as an argument to `Format()`. +// +// All the object has to do define an overload of `AbslFormatFlush()` for the +// sink, usually by adding a ADL-based free function in the same namespace as +// the sink: +// +// void AbslFormatFlush(MySink* dest, absl::string_view part); +// +// where `dest` is the pointer passed to `absl::Format()`. The function should +// append `part` to `dest`. +// // FormatRawSink does not own the passed sink object. The passed object must // outlive the FormatRawSink. class FormatRawSink { @@ -455,12 +490,13 @@ class FormatRawSink { // `absl::FormatRawSink` interface), using a format string and zero or more // additional arguments. // -// By default, `std::string` and `std::ostream` are supported as destination -// objects. If a `std::string` is used the formatted string is appended to it. +// By default, `std::string`, `std::ostream`, and `absl::Cord` are supported as +// destination objects. If a `std::string` is used the formatted string is +// appended to it. // -// `absl::Format()` is a generic version of `absl::StrFormat(), for custom -// sinks. The format string, like format strings for `StrFormat()`, is checked -// at compile-time. +// `absl::Format()` is a generic version of `absl::StrAppendFormat()`, for +// custom sinks. The format string, like format strings for `StrFormat()`, is +// checked at compile-time. // // On failure, this function returns `false` and the state of the sink is // unspecified. @@ -531,6 +567,246 @@ ABSL_MUST_USE_RESULT inline bool FormatUntyped( str_format_internal::UntypedFormatSpecImpl::Extract(format), args); } +//------------------------------------------------------------------------------ +// StrFormat Extensions +//------------------------------------------------------------------------------ +// +// AbslFormatConvert() +// +// The StrFormat library provides a customization API for formatting +// user-defined types using absl::StrFormat(). The API relies on detecting an +// overload in the user-defined type's namespace of a free (non-member) +// `AbslFormatConvert()` function, usually as a friend definition with the +// following signature: +// +// absl::FormatConvertResult<...> AbslFormatConvert( +// const X& value, +// const absl::FormatConversionSpec& spec, +// absl::FormatSink *sink); +// +// An `AbslFormatConvert()` overload for a type should only be declared in the +// same file and namespace as said type. +// +// The abstractions within this definition include: +// +// * An `absl::FormatConversionSpec` to specify the fields to pull from a +// user-defined type's format string +// * An `absl::FormatSink` to hold the converted string data during the +// conversion process. +// * An `absl::FormatConvertResult` to hold the status of the returned +// formatting operation +// +// The return type encodes all the conversion characters that your +// AbslFormatConvert() routine accepts. The return value should be {true}. +// A return value of {false} will result in `StrFormat()` returning +// an empty string. This result will be propagated to the result of +// `FormatUntyped`. +// +// Example: +// +// struct Point { +// // To add formatting support to `Point`, we simply need to add a free +// // (non-member) function `AbslFormatConvert()`. This method interprets +// // `spec` to print in the request format. The allowed conversion characters +// // can be restricted via the type of the result, in this example +// // string and integral formatting are allowed (but not, for instance +// // floating point characters like "%f"). You can add such a free function +// // using a friend declaration within the body of the class: +// friend absl::FormatConvertResult<absl::FormatConversionCharSet::kString | +// absl::FormatConversionCharSet::kIntegral> +// AbslFormatConvert(const Point& p, const absl::FormatConversionSpec& spec, +// absl::FormatSink* s) { +// if (spec.conversion_char() == absl::FormatConversionChar::s) { +// s->Append(absl::StrCat("x=", p.x, " y=", p.y)); +// } else { +// s->Append(absl::StrCat(p.x, ",", p.y)); +// } +// return {true}; +// } +// +// int x; +// int y; +// }; + +// clang-format off + +// FormatConversionChar +// +// Specifies the formatting character provided in the format string +// passed to `StrFormat()`. +enum class FormatConversionChar : uint8_t { + c, s, // text + d, i, o, u, x, X, // int + f, F, e, E, g, G, a, A, // float + n, p // misc +}; +// clang-format on + +// FormatConversionSpec +// +// Specifies modifications to the conversion of the format string, through use +// of one or more format flags in the source format string. +class FormatConversionSpec { + public: + // FormatConversionSpec::is_basic() + // + // Indicates that width and precision are not specified, and no additional + // flags are set for this conversion character in the format string. + bool is_basic() const { return impl_.is_basic(); } + + // FormatConversionSpec::has_left_flag() + // + // Indicates whether the result should be left justified for this conversion + // character in the format string. This flag is set through use of a '-' + // character in the format string. E.g. "%-s" + bool has_left_flag() const { return impl_.has_left_flag(); } + + // FormatConversionSpec::has_show_pos_flag() + // + // Indicates whether a sign column is prepended to the result for this + // conversion character in the format string, even if the result is positive. + // This flag is set through use of a '+' character in the format string. + // E.g. "%+d" + bool has_show_pos_flag() const { return impl_.has_show_pos_flag(); } + + // FormatConversionSpec::has_sign_col_flag() + // + // Indicates whether a mandatory sign column is added to the result for this + // conversion character. This flag is set through use of a space character + // (' ') in the format string. E.g. "% i" + bool has_sign_col_flag() const { return impl_.has_sign_col_flag(); } + + // FormatConversionSpec::has_alt_flag() + // + // Indicates whether an "alternate" format is applied to the result for this + // conversion character. Alternative forms depend on the type of conversion + // character, and unallowed alternatives are undefined. This flag is set + // through use of a '#' character in the format string. E.g. "%#h" + bool has_alt_flag() const { return impl_.has_alt_flag(); } + + // FormatConversionSpec::has_zero_flag() + // + // Indicates whether zeroes should be prepended to the result for this + // conversion character instead of spaces. This flag is set through use of the + // '0' character in the format string. E.g. "%0f" + bool has_zero_flag() const { return impl_.has_zero_flag(); } + + // FormatConversionSpec::conversion_char() + // + // Returns the underlying conversion character. + FormatConversionChar conversion_char() const { + return impl_.conversion_char(); + } + + // FormatConversionSpec::width() + // + // Returns the specified width (indicated through use of a non-zero integer + // value or '*' character) of the conversion character. If width is + // unspecified, it returns a negative value. + int width() const { return impl_.width(); } + + // FormatConversionSpec::precision() + // + // Returns the specified precision (through use of the '.' character followed + // by a non-zero integer value or '*' character) of the conversion character. + // If precision is unspecified, it returns a negative value. + int precision() const { return impl_.precision(); } + + private: + explicit FormatConversionSpec( + str_format_internal::FormatConversionSpecImpl impl) + : impl_(impl) {} + + friend str_format_internal::FormatConversionSpecImpl; + + absl::str_format_internal::FormatConversionSpecImpl impl_; +}; + +// Type safe OR operator for FormatConversionCharSet to allow accepting multiple +// conversion chars in custom format converters. +constexpr FormatConversionCharSet operator|(FormatConversionCharSet a, + FormatConversionCharSet b) { + return static_cast<FormatConversionCharSet>(static_cast<uint64_t>(a) | + static_cast<uint64_t>(b)); +} + +// FormatConversionCharSet +// +// Specifies the _accepted_ conversion types as a template parameter to +// FormatConvertResult for custom implementations of `AbslFormatConvert`. +// Note the helper predefined alias definitions (kIntegral, etc.) below. +enum class FormatConversionCharSet : uint64_t { + // text + c = str_format_internal::FormatConversionCharToConvInt('c'), + s = str_format_internal::FormatConversionCharToConvInt('s'), + // integer + d = str_format_internal::FormatConversionCharToConvInt('d'), + i = str_format_internal::FormatConversionCharToConvInt('i'), + o = str_format_internal::FormatConversionCharToConvInt('o'), + u = str_format_internal::FormatConversionCharToConvInt('u'), + x = str_format_internal::FormatConversionCharToConvInt('x'), + X = str_format_internal::FormatConversionCharToConvInt('X'), + // Float + f = str_format_internal::FormatConversionCharToConvInt('f'), + F = str_format_internal::FormatConversionCharToConvInt('F'), + e = str_format_internal::FormatConversionCharToConvInt('e'), + E = str_format_internal::FormatConversionCharToConvInt('E'), + g = str_format_internal::FormatConversionCharToConvInt('g'), + G = str_format_internal::FormatConversionCharToConvInt('G'), + a = str_format_internal::FormatConversionCharToConvInt('a'), + A = str_format_internal::FormatConversionCharToConvInt('A'), + // misc + n = str_format_internal::FormatConversionCharToConvInt('n'), + p = str_format_internal::FormatConversionCharToConvInt('p'), + + // Used for width/precision '*' specification. + kStar = static_cast<uint64_t>( + absl::str_format_internal::FormatConversionCharSetInternal::kStar), + // Some predefined values: + kIntegral = d | i | u | o | x | X, + kFloating = a | e | f | g | A | E | F | G, + kNumeric = kIntegral | kFloating, + kString = s, + kPointer = p, +}; + +// FormatSink +// +// An abstraction to which conversions write their string data. +// +class FormatSink { + public: + // Appends `count` copies of `ch`. + void Append(size_t count, char ch) { sink_->Append(count, ch); } + + void Append(string_view v) { sink_->Append(v); } + + // Appends the first `precision` bytes of `v`. If this is less than + // `width`, spaces will be appended first (if `left` is false), or + // after (if `left` is true) to ensure the total amount appended is + // at least `width`. + bool PutPaddedString(string_view v, int width, int precision, bool left) { + return sink_->PutPaddedString(v, width, precision, left); + } + + private: + friend str_format_internal::FormatSinkImpl; + explicit FormatSink(str_format_internal::FormatSinkImpl* s) : sink_(s) {} + str_format_internal::FormatSinkImpl* sink_; +}; + +// FormatConvertResult +// +// Indicates whether a call to AbslFormatConvert() was successful. +// This return type informs the StrFormat extension framework (through +// ADL but using the return type) of what conversion characters are supported. +// It is strongly discouraged to return {false}, as this will result in an +// empty string in StrFormat. +template <FormatConversionCharSet C> +struct FormatConvertResult { + bool value; +}; + ABSL_NAMESPACE_END } // namespace absl |