folly/folly/Format.h

/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * 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.
 */

//
// Docs: https://fburl.com/fbcref_format
//

/**
 * folly::format has been superseded by
 * [fmt](https://fmt.dev/latest/index.html). `#include <fmt/core.h>`
 *
 * format() performs text-formatting, similar to Python's str.format. The full
 * specification is on github:
 * https://github.com/facebook/folly/blob/main/folly/docs/Format.md
 *
 * @refcode folly/docs/examples/folly/Format.cpp
 * @file Format.h
 */

#pragma once
#define FOLLY_FORMAT_H_

#include <cstdio>
#include <ios>
#include <stdexcept>
#include <tuple>
#include <type_traits>

#include <folly/CPortability.h>
#include <folly/Conv.h>
#include <folly/FormatArg.h>
#include <folly/Range.h>
#include <folly/String.h>
#include <folly/Traits.h>

// Ignore shadowing warnings within this file, so includers can use -Wshadow.
FOLLY_PUSH_WARNING
FOLLY_GNU_DISABLE_WARNING(…)

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>
std::string svformat(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 { … };

struct BaseFormatterBase { … };

// BaseFormatterTuple suffices and is faster to compile than is std::tuple
template <size_t I, typename A>
struct BaseFormatterTupleIndexedValue { … };
template <typename, typename...>
struct BaseFormatterTuple;
BaseFormatterTuple<std::index_sequence<I...>, A...>;

template <typename Str>
struct BaseFormatterAppendToString { … };

inline void formatCheckIndex(size_t i, const FormatArg& arg, size_t max) { … }
} // namespace detail

/**
 * Formatter class.
 *
 * Note that this class is tricky, as it keeps *references* to its lvalue
 * arguments (while it takes ownership of the temporaries), and it doesn't
 * copy the passed-in format string. Thankfully, you can't use this
 * directly, you have to use format(...) below.
 */

/* BaseFormatter class.
 * Overridable behaviors:
 * You may override the actual formatting of positional parameters in
 * `doFormatArg`. The Formatter class provides the default implementation.
 *
 * You may also override `recordUsedArg`. This override point was added to
 * permit static analysis of format strings, when it is inconvenient or
 * impossible to instantiate a BaseFormatter with the correct storage. If
 * overriding, the return type must be std::true_type.
 */
template <class Derived, bool containerMode, class Indices, class... Args>
class BaseFormatterImpl;
BaseFormatterImpl<Derived, containerMode, std::index_sequence<I...>, Args...>;
BaseFormatter;

template <bool containerMode, class... Args>
class Formatter : public BaseFormatter<
                      Formatter<containerMode, Args...>,
                      containerMode,
                      Args...> { … };

namespace detail {
template <typename Out>
struct FormatterOstreamInsertionWriterFn { … };
} // namespace detail

/**
 * Formatter objects can be written to streams.
 */
template <class C, class CT, bool containerMode, class... Args>
std::ostream& operator<<(
    std::basic_ostream<C, CT>& out,
    const Formatter<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>
[[deprecated(
    "Use fmt::format instead of folly::format for better performance, build "
    "times and compatibility with std::format")]] //
Formatter<false, Args...>
format(StringPiece fmt, 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) { … }

/**
 * 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:
 * sformat("{0[hello]} {0[answer]}", map);
 *
 * svformat("{hello} {answer}", map);
 *
 * but the latter is cleaner.
 */
template <class Container>
[[deprecated(
    "Use fmt::format instead of folly::svformat for better performance, build "
    "times and compatibility with std::format")]] //
inline std::string
svformat(StringPiece fmt, Container&& container) { … }

/**
 * Exception class thrown when a format key is not found in the given
 * associative container keyed by strings. We inherit std::out_of_range for
 * compatibility with callers that expect exception to be thrown directly
 * by std::map or std::unordered_map.
 *
 * Having the key be at the end of the message string, we can access it by
 * simply adding its offset to what(). Not storing separate std::string key
 * makes the exception type small and noexcept-copyable like std::out_of_range,
 * and therefore able to fit in-situ in exception_wrapper.
 */
class FOLLY_EXPORT FormatKeyNotFoundException : public std::out_of_range { … };

/**
 * 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 { … };
} // namespace detail

template <class Container, class Value>
detail::DefaultValueWrapper<Container, Value> defaulted(
    const Container& c, const Value& 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) { … }

/**
 * 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, bool containerMode, class... Args>
void formatFormatter(
    const Formatter<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 { … };

IsFormatter<T, typename std::enable_if<std::is_same<typename T::IsFormatter, detail::FormatterTag>::value>::type>;
} // namespace detail

} // namespace folly

#include <folly/Format-inl.h>

FOLLY_POP_WARNING