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/*
* Copyright 2016 Facebook, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#pragma once
#define FOLLY_FORMAT_H_
#include <cstdio>
#include <tuple>
#include <type_traits>
#include <folly/Conv.h>
#include <folly/Range.h>
#include <folly/Traits.h>
#include <folly/String.h>
#include <folly/FormatArg.h>
// Ignore shadowing warnings within this file, so includers can use -Wshadow.
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wshadow"
namespace folly {
// forward declarations
template <bool containerMode, class... Args> class Formatter;
template <class... Args>
Formatter<false, Args...> format(StringPiece fmt, Args&&... args);
template <class C>
Formatter<true, C> vformat(StringPiece fmt, C&& container);
template <class T, class Enable=void> class FormatValue;
// meta-attribute to identify formatters in this sea of template weirdness
namespace detail {
class FormatterTag {};
};
/**
* Formatter class.
*
* Note that this class is tricky, as it keeps *references* to its arguments
* (and doesn't copy the passed-in format string). Thankfully, you can't use
* this directly, you have to use format(...) below.
*/
/* BaseFormatter class. Currently, the only behavior that can be
* overridden is the actual formatting of positional parameters in
* `doFormatArg`. The Formatter class provides the default implementation.
*/
template <class Derived, bool containerMode, class... Args>
class BaseFormatter {
public:
/**
* Append to output. out(StringPiece sp) may be called (more than once)
*/
template <class Output>
void operator()(Output& out) const;
/**
* Append to a string.
*/
template <class Str>
typename std::enable_if<IsSomeString<Str>::value>::type
appendTo(Str& str) const {
auto appender = [&str] (StringPiece s) { str.append(s.data(), s.size()); };
(*this)(appender);
}
/**
* Conversion to string
*/
std::string str() const {
std::string s;
appendTo(s);
return s;
}
/**
* Conversion to fbstring
*/
fbstring fbstr() const {
fbstring s;
appendTo(s);
return s;
}
/**
* metadata to identify generated children of BaseFormatter
*/
typedef detail::FormatterTag IsFormatter;
typedef BaseFormatter BaseType;
private:
typedef std::tuple<FormatValue<
typename std::decay<Args>::type>...> ValueTuple;
static constexpr size_t valueCount = std::tuple_size<ValueTuple>::value;
template <size_t K, class Callback>
typename std::enable_if<K == valueCount>::type
doFormatFrom(size_t i, FormatArg& arg, Callback& /*cb*/) const {
arg.error("argument index out of range, max=", i);
}
template <size_t K, class Callback>
typename std::enable_if<(K < valueCount)>::type
doFormatFrom(size_t i, FormatArg& arg, Callback& cb) const {
if (i == K) {
static_cast<const Derived*>(this)->template doFormatArg<K>(arg, cb);
} else {
doFormatFrom<K+1>(i, arg, cb);
}
}
template <class Callback>
void doFormat(size_t i, FormatArg& arg, Callback& cb) const {
return doFormatFrom<0>(i, arg, cb);
}
template <size_t K>
typename std::enable_if<K == valueCount, int>::type
getSizeArgFrom(size_t i, const FormatArg& arg) const {
arg.error("argument index out of range, max=", i);
}
template <class T>
typename std::enable_if<std::is_integral<T>::value &&
!std::is_same<T, bool>::value, int>::type
getValue(const FormatValue<T>& format, const FormatArg&) const {
return static_cast<int>(format.getValue());
}
template <class T>
typename std::enable_if<!std::is_integral<T>::value ||
std::is_same<T, bool>::value, int>::type
getValue(const FormatValue<T>&, const FormatArg& arg) const {
arg.error("dynamic field width argument must be integral");
}
template <size_t K>
typename std::enable_if<K < valueCount, int>::type
getSizeArgFrom(size_t i, const FormatArg& arg) const {
if (i == K) {
return getValue(std::get<K>(values_), arg);
}
return getSizeArgFrom<K+1>(i, arg);
}
int getSizeArg(size_t i, const FormatArg& arg) const {
return getSizeArgFrom<0>(i, arg);
}
StringPiece str_;
protected:
explicit BaseFormatter(StringPiece str, Args&&... args);
// Not copyable
BaseFormatter(const BaseFormatter&) = delete;
BaseFormatter& operator=(const BaseFormatter&) = delete;
// Movable, but the move constructor and assignment operator are private,
// for the exclusive use of format() (below). This way, you can't create
// a Formatter object, but can handle references to it (for streaming,
// conversion to string, etc) -- which is good, as Formatter objects are
// dangerous (they hold references, possibly to temporaries)
BaseFormatter(BaseFormatter&&) = default;
BaseFormatter& operator=(BaseFormatter&&) = default;
ValueTuple values_;
};
template <bool containerMode, class... Args>
class Formatter : public BaseFormatter<Formatter<containerMode, Args...>,
containerMode,
Args...> {
private:
explicit Formatter(StringPiece& str, Args&&... args)
: BaseFormatter<Formatter<containerMode, Args...>,
containerMode,
Args...>(str, std::forward<Args>(args)...) {}
template <size_t K, class Callback>
void doFormatArg(FormatArg& arg, Callback& cb) const {
std::get<K>(this->values_).format(arg, cb);
}
friend class BaseFormatter<Formatter<containerMode, Args...>,
containerMode,
Args...>;
template <class... A>
friend Formatter<false, A...> format(StringPiece fmt, A&&... arg);
template <class C>
friend Formatter<true, C> vformat(StringPiece fmt, C&& container);
};
/**
* Formatter objects can be written to streams.
*/
template<bool containerMode, class... Args>
std::ostream& operator<<(std::ostream& out,
const Formatter<containerMode, Args...>& formatter) {
auto writer = [&out] (StringPiece sp) { out.write(sp.data(), sp.size()); };
formatter(writer);
return out;
}
/**
* Formatter objects can be written to stdio FILEs.
*/
template <class Derived, bool containerMode, class... Args>
void writeTo(FILE* fp,
const BaseFormatter<Derived, containerMode, Args...>& formatter);
/**
* Create a formatter object.
*
* std::string formatted = format("{} {}", 23, 42).str();
* LOG(INFO) << format("{} {}", 23, 42);
* writeTo(stdout, format("{} {}", 23, 42));
*/
template <class... Args>
Formatter<false, Args...> format(StringPiece fmt, Args&&... args) {
return Formatter<false, Args...>(
fmt, std::forward<Args>(args)...);
}
/**
* Like format(), but immediately returns the formatted string instead of an
* intermediate format object.
*/
template <class... Args>
inline std::string sformat(StringPiece fmt, Args&&... args) {
return format(fmt, std::forward<Args>(args)...).str();
}
/**
* Create a formatter object that takes one argument (of container type)
* and uses that container to get argument values from.
*
* std::map<string, string> map { {"hello", "world"}, {"answer", "42"} };
*
* The following are equivalent:
* format("{0[hello]} {0[answer]}", map);
*
* vformat("{hello} {answer}", map);
*
* but the latter is cleaner.
*/
template <class Container>
Formatter<true, Container> vformat(StringPiece fmt, Container&& container) {
return Formatter<true, Container>(
fmt, std::forward<Container>(container));
}
/**
* Like vformat(), but immediately returns the formatted string instead of an
* intermediate format object.
*/
template <class Container>
inline std::string svformat(StringPiece fmt, Container&& container) {
return vformat(fmt, std::forward<Container>(container)).str();
}
/**
* Wrap a sequence or associative container so that out-of-range lookups
* return a default value rather than throwing an exception.
*
* Usage:
* format("[no_such_key"], defaulted(map, 42)) -> 42
*/
namespace detail {
template <class Container, class Value> struct DefaultValueWrapper {
DefaultValueWrapper(const Container& container, const Value& defaultValue)
: container(container),
defaultValue(defaultValue) {
}
const Container& container;
const Value& defaultValue;
};
} // namespace
template <class Container, class Value>
detail::DefaultValueWrapper<Container, Value>
defaulted(const Container& c, const Value& v) {
return detail::DefaultValueWrapper<Container, Value>(c, v);
}
/**
* Append formatted output to a string.
*
* std::string foo;
* format(&foo, "{} {}", 42, 23);
*
* Shortcut for toAppend(format(...), &foo);
*/
template <class Str, class... Args>
typename std::enable_if<IsSomeString<Str>::value>::type
format(Str* out, StringPiece fmt, Args&&... args) {
format(fmt, std::forward<Args>(args)...).appendTo(*out);
}
/**
* Append vformatted output to a string.
*/
template <class Str, class Container>
typename std::enable_if<IsSomeString<Str>::value>::type
vformat(Str* out, StringPiece fmt, Container&& container) {
vformat(fmt, std::forward<Container>(container)).appendTo(*out);
}
/**
* Utilities for all format value specializations.
*/
namespace format_value {
/**
* Format a string in "val", obeying appropriate alignment, padding, width,
* and precision. Treats Align::DEFAULT as Align::LEFT, and
* Align::PAD_AFTER_SIGN as Align::RIGHT; use formatNumber for
* number-specific formatting.
*/
template <class FormatCallback>
void formatString(StringPiece val, FormatArg& arg, FormatCallback& cb);
/**
* Format a number in "val"; the first prefixLen characters form the prefix
* (sign, "0x" base prefix, etc) which must be left-aligned if the alignment
* is Align::PAD_AFTER_SIGN. Treats Align::DEFAULT as Align::LEFT. Ignores
* arg.precision, as that has a different meaning for numbers (not "maximum
* field width")
*/
template <class FormatCallback>
void formatNumber(StringPiece val, int prefixLen, FormatArg& arg,
FormatCallback& cb);
/**
* Format a Formatter object recursively. Behaves just like
* formatString(fmt.str(), arg, cb); but avoids creating a temporary
* string if possible.
*/
template <class FormatCallback,
class Derived,
bool containerMode,
class... Args>
void formatFormatter(
const BaseFormatter<Derived, containerMode, Args...>& formatter,
FormatArg& arg,
FormatCallback& cb);
} // namespace format_value
/*
* Specialize folly::FormatValue for your type.
*
* FormatValue<T> is constructed with a (reference-collapsed) T&&, which is
* guaranteed to stay alive until the FormatValue object is destroyed, so you
* may keep a reference (or pointer) to it instead of making a copy.
*
* You must define
* template <class Callback>
* void format(FormatArg& arg, Callback& cb) const;
* with the following semantics: format the value using the given argument.
*
* arg is given by non-const reference for convenience -- it won't be reused,
* so feel free to modify it in place if necessary. (For example, wrap an
* existing conversion but change the default, or remove the "key" when
* extracting an element from a container)
*
* Call the callback to append data to the output. You may call the callback
* as many times as you'd like (or not at all, if you want to output an
* empty string)
*/
namespace detail {
template <class T, class Enable = void>
struct IsFormatter : public std::false_type {};
template <class T>
struct IsFormatter<
T,
typename std::enable_if<
std::is_same<typename T::IsFormatter, detail::FormatterTag>::value>::
type> : public std::true_type {};
} // folly::detail
// Deprecated API. formatChecked() et. al. now behave identically to their
// non-Checked counterparts.
template <class... Args>
Formatter<false, Args...> formatChecked(StringPiece fmt, Args&&... args) {
return format(fmt, std::forward<Args>(args)...);
}
template <class... Args>
inline std::string sformatChecked(StringPiece fmt, Args&&... args) {
return formatChecked(fmt, std::forward<Args>(args)...).str();
}
template <class Container>
Formatter<true, Container> vformatChecked(StringPiece fmt,
Container&& container) {
return vformat(fmt, std::forward<Container>(container));
}
template <class Container>
inline std::string svformatChecked(StringPiece fmt, Container&& container) {
return vformatChecked(fmt, std::forward<Container>(container)).str();
}
template <class Str, class... Args>
typename std::enable_if<IsSomeString<Str>::value>::type
formatChecked(Str* out, StringPiece fmt, Args&&... args) {
formatChecked(fmt, std::forward<Args>(args)...).appendTo(*out);
}
template <class Str, class Container>
typename std::enable_if<IsSomeString<Str>::value>::type
vformatChecked(Str* out, StringPiece fmt, Container&& container) {
vformatChecked(fmt, std::forward<Container>(container)).appendTo(*out);
}
} // namespace folly
#include <folly/Format-inl.h>
#pragma GCC diagnostic pop
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