diff options
Diffstat (limited to 'absl/strings/str_cat.h')
| -rw-r--r-- | absl/strings/str_cat.h | 53 |
1 files changed, 50 insertions, 3 deletions
diff --git a/absl/strings/str_cat.h b/absl/strings/str_cat.h index a94bc5df..730b4d8c 100644 --- a/absl/strings/str_cat.h +++ b/absl/strings/str_cat.h @@ -48,6 +48,40 @@ // `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_ @@ -57,9 +91,12 @@ #include <cstdint> #include <string> #include <type_traits> +#include <utility> #include <vector> #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" @@ -205,8 +242,10 @@ 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. +// `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: @@ -255,6 +294,13 @@ class AlphaNum { : piece_(NullSafeStringView(c_str)) {} // NOLINT(runtime/explicit) AlphaNum(absl::string_view pc) : piece_(pc) {} // NOLINT(runtime/explicit) + template <typename T, typename = typename std::enable_if< + strings_internal::HasAbslStringify<T>::value>::type> + AlphaNum( // NOLINT(runtime/explicit) + const T& v, // NOLINT(runtime/explicit) + strings_internal::StringifySink&& sink = {}) // NOLINT(runtime/explicit) + : piece_(strings_internal::ExtractStringification(sink, v)) {} + template <typename Allocator> AlphaNum( // NOLINT(runtime/explicit) const std::basic_string<char, std::char_traits<char>, Allocator>& str) @@ -274,7 +320,8 @@ 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)) {} |