2 * Copyright 2016 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
17 #ifndef FOLLY_FORMAT_H_
18 #define FOLLY_FORMAT_H_
22 #include <type_traits>
24 #include <folly/Conv.h>
25 #include <folly/Range.h>
26 #include <folly/Traits.h>
27 #include <folly/String.h>
28 #include <folly/FormatArg.h>
30 // Ignore shadowing warnings within this file, so includers can use -Wshadow.
31 #pragma GCC diagnostic push
32 #pragma GCC diagnostic ignored "-Wshadow"
36 // forward declarations
37 template <bool containerMode, class... Args> class Formatter;
38 template <class... Args>
39 Formatter<false, Args...> format(StringPiece fmt, Args&&... args);
41 Formatter<true, C> vformat(StringPiece fmt, C&& container);
42 template <class T, class Enable=void> class FormatValue;
44 // meta-attribute to identify formatters in this sea of template weirdness
46 class FormatterTag {};
52 * Note that this class is tricky, as it keeps *references* to its arguments
53 * (and doesn't copy the passed-in format string). Thankfully, you can't use
54 * this directly, you have to use format(...) below.
57 /* BaseFormatter class. Currently, the only behavior that can be
58 * overridden is the actual formatting of positional parameters in
59 * `doFormatArg`. The Formatter class provides the default implementation.
61 template <class Derived, bool containerMode, class... Args>
65 * Append to output. out(StringPiece sp) may be called (more than once)
67 template <class Output>
68 void operator()(Output& out) const;
74 typename std::enable_if<IsSomeString<Str>::value>::type
75 appendTo(Str& str) const {
76 auto appender = [&str] (StringPiece s) { str.append(s.data(), s.size()); };
81 * Conversion to string
83 std::string str() const {
90 * Conversion to fbstring
92 fbstring fbstr() const {
99 * metadata to identify generated children of BaseFormatter
101 typedef detail::FormatterTag IsFormatter;
102 typedef BaseFormatter BaseType;
105 typedef std::tuple<FormatValue<
106 typename std::decay<Args>::type>...> ValueTuple;
107 static constexpr size_t valueCount = std::tuple_size<ValueTuple>::value;
109 template <size_t K, class Callback>
110 typename std::enable_if<K == valueCount>::type
111 doFormatFrom(size_t i, FormatArg& arg, Callback& /*cb*/) const {
112 arg.error("argument index out of range, max=", i);
115 template <size_t K, class Callback>
116 typename std::enable_if<(K < valueCount)>::type
117 doFormatFrom(size_t i, FormatArg& arg, Callback& cb) const {
119 static_cast<const Derived*>(this)->template doFormatArg<K>(arg, cb);
121 doFormatFrom<K+1>(i, arg, cb);
125 template <class Callback>
126 void doFormat(size_t i, FormatArg& arg, Callback& cb) const {
127 return doFormatFrom<0>(i, arg, cb);
131 typename std::enable_if<K == valueCount, int>::type
132 getSizeArgFrom(size_t i, const FormatArg& arg) const {
133 arg.error("argument index out of range, max=", i);
137 typename std::enable_if<std::is_integral<T>::value &&
138 !std::is_same<T, bool>::value, int>::type
139 getValue(const FormatValue<T>& format, const FormatArg&) const {
140 return static_cast<int>(format.getValue());
144 typename std::enable_if<!std::is_integral<T>::value ||
145 std::is_same<T, bool>::value, int>::type
146 getValue(const FormatValue<T>&, const FormatArg& arg) const {
147 arg.error("dynamic field width argument must be integral");
151 typename std::enable_if<K < valueCount, int>::type
152 getSizeArgFrom(size_t i, const FormatArg& arg) const {
154 return getValue(std::get<K>(values_), arg);
156 return getSizeArgFrom<K+1>(i, arg);
159 int getSizeArg(size_t i, const FormatArg& arg) const {
160 return getSizeArgFrom<0>(i, arg);
166 explicit BaseFormatter(StringPiece str, Args&&... args);
169 BaseFormatter(const BaseFormatter&) = delete;
170 BaseFormatter& operator=(const BaseFormatter&) = delete;
172 // Movable, but the move constructor and assignment operator are private,
173 // for the exclusive use of format() (below). This way, you can't create
174 // a Formatter object, but can handle references to it (for streaming,
175 // conversion to string, etc) -- which is good, as Formatter objects are
176 // dangerous (they hold references, possibly to temporaries)
177 BaseFormatter(BaseFormatter&&) = default;
178 BaseFormatter& operator=(BaseFormatter&&) = default;
183 template <bool containerMode, class... Args>
184 class Formatter : public BaseFormatter<Formatter<containerMode, Args...>,
188 explicit Formatter(StringPiece& str, Args&&... args)
189 : BaseFormatter<Formatter<containerMode, Args...>,
191 Args...>(str, std::forward<Args>(args)...) {}
193 template <size_t K, class Callback>
194 void doFormatArg(FormatArg& arg, Callback& cb) const {
195 std::get<K>(this->values_).format(arg, cb);
198 friend class BaseFormatter<Formatter<containerMode, Args...>,
202 template <class... A>
203 friend Formatter<false, A...> format(StringPiece fmt, A&&... arg);
205 friend Formatter<true, C> vformat(StringPiece fmt, C&& container);
209 * Formatter objects can be written to streams.
211 template<bool containerMode, class... Args>
212 std::ostream& operator<<(std::ostream& out,
213 const Formatter<containerMode, Args...>& formatter) {
214 auto writer = [&out] (StringPiece sp) { out.write(sp.data(), sp.size()); };
220 * Formatter objects can be written to stdio FILEs.
222 template <class Derived, bool containerMode, class... Args>
223 void writeTo(FILE* fp,
224 const BaseFormatter<Derived, containerMode, Args...>& formatter);
227 * Create a formatter object.
229 * std::string formatted = format("{} {}", 23, 42).str();
230 * LOG(INFO) << format("{} {}", 23, 42);
231 * writeTo(stdout, format("{} {}", 23, 42));
233 template <class... Args>
234 Formatter<false, Args...> format(StringPiece fmt, Args&&... args) {
235 return Formatter<false, Args...>(
236 fmt, std::forward<Args>(args)...);
240 * Like format(), but immediately returns the formatted string instead of an
241 * intermediate format object.
243 template <class... Args>
244 inline std::string sformat(StringPiece fmt, Args&&... args) {
245 return format(fmt, std::forward<Args>(args)...).str();
249 * Create a formatter object that takes one argument (of container type)
250 * and uses that container to get argument values from.
252 * std::map<string, string> map { {"hello", "world"}, {"answer", "42"} };
254 * The following are equivalent:
255 * format("{0[hello]} {0[answer]}", map);
257 * vformat("{hello} {answer}", map);
259 * but the latter is cleaner.
261 template <class Container>
262 Formatter<true, Container> vformat(StringPiece fmt, Container&& container) {
263 return Formatter<true, Container>(
264 fmt, std::forward<Container>(container));
268 * Like vformat(), but immediately returns the formatted string instead of an
269 * intermediate format object.
271 template <class Container>
272 inline std::string svformat(StringPiece fmt, Container&& container) {
273 return vformat(fmt, std::forward<Container>(container)).str();
277 * Wrap a sequence or associative container so that out-of-range lookups
278 * return a default value rather than throwing an exception.
281 * format("[no_such_key"], defaulted(map, 42)) -> 42
284 template <class Container, class Value> struct DefaultValueWrapper {
285 DefaultValueWrapper(const Container& container, const Value& defaultValue)
286 : container(container),
287 defaultValue(defaultValue) {
290 const Container& container;
291 const Value& defaultValue;
295 template <class Container, class Value>
296 detail::DefaultValueWrapper<Container, Value>
297 defaulted(const Container& c, const Value& v) {
298 return detail::DefaultValueWrapper<Container, Value>(c, v);
302 * Append formatted output to a string.
305 * format(&foo, "{} {}", 42, 23);
307 * Shortcut for toAppend(format(...), &foo);
309 template <class Str, class... Args>
310 typename std::enable_if<IsSomeString<Str>::value>::type
311 format(Str* out, StringPiece fmt, Args&&... args) {
312 format(fmt, std::forward<Args>(args)...).appendTo(*out);
316 * Append vformatted output to a string.
318 template <class Str, class Container>
319 typename std::enable_if<IsSomeString<Str>::value>::type
320 vformat(Str* out, StringPiece fmt, Container&& container) {
321 vformat(fmt, std::forward<Container>(container)).appendTo(*out);
325 * Utilities for all format value specializations.
327 namespace format_value {
330 * Format a string in "val", obeying appropriate alignment, padding, width,
331 * and precision. Treats Align::DEFAULT as Align::LEFT, and
332 * Align::PAD_AFTER_SIGN as Align::RIGHT; use formatNumber for
333 * number-specific formatting.
335 template <class FormatCallback>
336 void formatString(StringPiece val, FormatArg& arg, FormatCallback& cb);
339 * Format a number in "val"; the first prefixLen characters form the prefix
340 * (sign, "0x" base prefix, etc) which must be left-aligned if the alignment
341 * is Align::PAD_AFTER_SIGN. Treats Align::DEFAULT as Align::LEFT. Ignores
342 * arg.precision, as that has a different meaning for numbers (not "maximum
345 template <class FormatCallback>
346 void formatNumber(StringPiece val, int prefixLen, FormatArg& arg,
351 * Format a Formatter object recursively. Behaves just like
352 * formatString(fmt.str(), arg, cb); but avoids creating a temporary
353 * string if possible.
355 template <class FormatCallback,
359 void formatFormatter(
360 const BaseFormatter<Derived, containerMode, Args...>& formatter,
364 } // namespace format_value
367 * Specialize folly::FormatValue for your type.
369 * FormatValue<T> is constructed with a (reference-collapsed) T&&, which is
370 * guaranteed to stay alive until the FormatValue object is destroyed, so you
371 * may keep a reference (or pointer) to it instead of making a copy.
374 * template <class Callback>
375 * void format(FormatArg& arg, Callback& cb) const;
376 * with the following semantics: format the value using the given argument.
378 * arg is given by non-const reference for convenience -- it won't be reused,
379 * so feel free to modify it in place if necessary. (For example, wrap an
380 * existing conversion but change the default, or remove the "key" when
381 * extracting an element from a container)
383 * Call the callback to append data to the output. You may call the callback
384 * as many times as you'd like (or not at all, if you want to output an
390 template <class T, class Enable = void>
391 struct IsFormatter : public std::false_type {};
396 typename std::enable_if<
397 std::is_same<typename T::IsFormatter, detail::FormatterTag>::value>::
398 type> : public std::true_type {};
401 // Deprecated API. formatChecked() et. al. now behave identically to their
402 // non-Checked counterparts.
403 template <class... Args>
404 Formatter<false, Args...> formatChecked(StringPiece fmt, Args&&... args) {
405 return format(fmt, std::forward<Args>(args)...);
407 template <class... Args>
408 inline std::string sformatChecked(StringPiece fmt, Args&&... args) {
409 return formatChecked(fmt, std::forward<Args>(args)...).str();
411 template <class Container>
412 Formatter<true, Container> vformatChecked(StringPiece fmt,
413 Container&& container) {
414 return vformat(fmt, std::forward<Container>(container));
416 template <class Container>
417 inline std::string svformatChecked(StringPiece fmt, Container&& container) {
418 return vformatChecked(fmt, std::forward<Container>(container)).str();
420 template <class Str, class... Args>
421 typename std::enable_if<IsSomeString<Str>::value>::type
422 formatChecked(Str* out, StringPiece fmt, Args&&... args) {
423 formatChecked(fmt, std::forward<Args>(args)...).appendTo(*out);
425 template <class Str, class Container>
426 typename std::enable_if<IsSomeString<Str>::value>::type
427 vformatChecked(Str* out, StringPiece fmt, Container&& container) {
428 vformatChecked(fmt, std::forward<Container>(container)).appendTo(*out);
433 #include <folly/Format-inl.h>
435 #pragma GCC diagnostic pop
437 #endif /* FOLLY_FORMAT_H_ */