Feature/basic string

include/boost/hana/fwd/basic_string.hpp

@@ -0,0 +1,276 @@
+/*!
+@file
+Forward declares `boost::hana::basic_string`.
+
+@copyright Louis Dionne 2013-2017
+Distributed under the Boost Software License, Version 1.0.
+(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
+ */
+
+#ifndef BOOST_HANA_FWD_BASIC_STRING_HPP
+#define BOOST_HANA_FWD_BASIC_STRING_HPP
+
+#include <boost/hana/config.hpp>
+#include <boost/hana/fwd/core/make.hpp>
+#include <boost/hana/fwd/core/to.hpp>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+#ifdef BOOST_HANA_DOXYGEN_INVOKED
+    //! @ingroup group-datatypes
+    //! Compile-time basic_string<Ch>.
+    //!
+    //! Conceptually, a `hana::string` is like a tuple holding
+    //! `integral_constant`s of underlying type `char`. However, the
+    //! interface of `hana::string` is not as rich as that of a tuple,
+    //! because a string can only hold compile-time characters as opposed
+    //! to any kind of object.
+    //!
+    //! Compile-time strings are used for simple purposes like being keys in a
+    //! `hana::map` or tagging the members of a `Struct`. However, you might
+    //! find that `hana::string` does not provide enough functionality to be
+    //! used as a full-blown compile-time string implementation (e.g. regexp
+    //! matching or substring finding). Indeed, providing a comprehensive
+    //! string interface is a lot of job, and it is out of the scope of the
+    //! library for the time being.
+    //!
+    //!
+    //! @note
+    //! The representation of `hana::basic_string` takes character type
+    //! template parameters are `char`s.
+    //! The proper way to access the contents of
+    //! a `hana::string` as character constants is to use `hana::unpack`,
+    //! `.c_str()` or `hana::to<ChT const*>`, as documented below. More
+    //! details [in the tutorial](@ref tutorial-containers-types).
+    //!
+    //!
+    //! Modeled concepts
+    //! ----------------
+    //! For most purposes, a `hana::basic_string<ChT>` is functionally
+    //! equivalent to a tuple holding `Constant`s of underlying type `ChT`.
+    //!
+    //! 1. `Comparable`\n
+    //! Two strings are equal if and only if they have the same number of
+    //! characters and characters at corresponding indices are equal.
+    //! @include example/string/comparable.cpp
+    //!
+    //! 2. `Orderable`\n
+    //! The total order implemented for `Orderable` is the usual
+    //! lexicographical comparison of strings.
+    //! @include example/string/orderable.cpp
+    //!
+    //! 3. `Monoid`\n
+    //! Strings form a monoid under concatenation, with the neutral element
+    //! being the empty string.
+    //! @include example/string/monoid.cpp
+    //!
+    //! 4. `Foldable`\n
+    //! Folding a string is equivalent to folding the sequence of its
+    //! characters.
+    //! @include example/string/foldable.cpp
+    //!
+    //! 5. `Iterable`\n
+    //! Iterating over a string is equivalent to iterating over the sequence
+    //! of its characters. Also note that `operator[]` can be used instead of
+    //! the `at` function.
+    //! @include example/string/iterable.cpp
+    //!
+    //! 6. `Searchable`\n
+    //! Searching through a string is equivalent to searching through the
+    //! sequence of its characters.
+    //! @include example/string/searchable.cpp
+    //!
+    //! 7. `Hashable`\n
+    //! The hash of a compile-time string is a type uniquely representing
+    //! that string.
+    //! @include example/string/hashable.cpp
+    //!
+    //!
+    //! Conversion to `char const*`
+    //! ---------------------------
+    //! A `hana::string` can be converted to a `constexpr` null-delimited
+    //! string of type `char const*` by using the `c_str()` method or
+    //! `hana::to<char const*>`. This makes it easy to turn a compile-time
+    //! string into a runtime string. However, note that this conversion is
+    //! not an embedding, because `char const*` does not model the same
+    //! concepts as `hana::string` does.
+    //! @include example/string/to.cpp
+    //!
+    //! Conversion from any Constant holding a `char const*`
+    //! ----------------------------------------------------
+    //! A `hana::string` can be created from any `Constant` whose underlying
+    //! value is convertible to a `char const*` by using `hana::to`. The
+    //! contents of the `char const*` are used to build the content of the
+    //! `hana::string`.
+    //! @include example/string/from_c_str.cpp
+    //!
+    //! Rationale for `hana::string` not being a `Constant` itself
+    //! ----------------------------------------------------------
+    //! The underlying type held by a `hana::string` could be either `char const*`
+    //! or some other constexpr-enabled string-like container. In the first case,
+    //! `hana::string` can not be a `Constant` because the models of several
+    //! concepts would not be respected by the underlying type, causing `value`
+    //! not to be structure-preserving. Providing an underlying value of
+    //! constexpr-enabled string-like container type like `std::string_view`
+    //! would be great, but that's a bit complicated for the time being.
+    template <typename Ch, Ch...>
+    struct basic_string {
+        // Default-construct a `hana::basic_string`; no-op since `hana::basic_string` is stateless.
+        constexpr basic_string() = default;
+
+        // Copy-construct a `hana::basic_string`; no-op since `hana::basic_string` is stateless.
+        constexpr basic_string(basic_string const&) = default;
+
+        //! Equivalent to `hana::equal`
+        template <typename X, typename Y>
+        friend constexpr auto operator==(X&& x, Y&& y);
+
+        //! Equivalent to `hana::not_equal`
+        template <typename X, typename Y>
+        friend constexpr auto operator!=(X&& x, Y&& y);
+
+        //! Equivalent to `hana::less`
+        template <typename X, typename Y>
+        friend constexpr auto operator<(X&& x, Y&& y);
+
+        //! Equivalent to `hana::greater`
+        template <typename X, typename Y>
+        friend constexpr auto operator>(X&& x, Y&& y);
+
+        //! Equivalent to `hana::less_equal`
+        template <typename X, typename Y>
+        friend constexpr auto operator<=(X&& x, Y&& y);
+
+        //! Equivalent to `hana::greater_equal`
+        template <typename X, typename Y>
+        friend constexpr auto operator>=(X&& x, Y&& y);
+
+        //! Performs concatenation; equivalent to `hana::plus`
+        template <typename X, typename Y>
+        friend constexpr auto operator+(X&& x, Y&& y);
+
+        //! Equivalent to `hana::at`
+        template <typename N>
+        constexpr decltype(auto) operator[](N&& n);
+
+        //! Returns a null-delimited C-style string.
+        static constexpr Ch const* c_str();
+    };
+#else
+    template <typename CharT, CharT ...s>
+    struct basic_string;
+#endif
+
+    //! Tag representing a compile-time string.
+    //! @relates hana::string
+    template <typename CharT>
+    struct basic_string_tag { };
+
+#ifdef BOOST_HANA_DOXYGEN_INVOKED
+    //! Create a compile-time `hana::string` from a parameter pack of `char`
+    //! `integral_constant`s.
+    //! @relates hana::string
+    //!
+    //! Given zero or more `integral_constant`s of underlying type `char`,
+    //! `make<string_tag>` creates a `hana::string` containing those characters.
+    //! This is provided mostly for consistency with the rest of the library,
+    //! as `hana::string_c` is more convenient to use in most cases.
+    //!
+    //!
+    //! Example
+    //! -------
+    //! @include example/string/make.cpp
+    template <typename Ch>
+    constexpr auto make<basic_string_tag<Ch>> = [](auto&& ...chars) {
+        return basic_string<Ch>{};
+    };
+#endif
+
+    //! Alias to `make<string_tag>`; provided for convenience.
+    //! @relates hana::string
+    template <typename CharT>
+    constexpr auto make_basic_string = make<basic_string_tag<CharT>>;
+
+    //! Equivalent to `to<string_tag>`; provided for convenience.
+    //! @relates hana::string
+    template <typename CharT>
+    constexpr auto to_basic_string = to<basic_string_tag<CharT>>;
+
+    //! Create a compile-time string from a parameter pack of characters.
+    //! @relates hana::string
+    //!
+    //!
+    //! Example
+    //! -------
+    //! @include example/string/string_c.cpp
+#ifdef BOOST_HANA_DOXYGEN_INVOKED
+    template <typename Ch, Ch ...s>
+    constexpr basic_string<Ch, s...> basic_string_c{};
+#else
+    template <typename CharT, CharT ...s>
+    constexpr basic_string<CharT, s...> basic_string_c{};
+#endif
+
+    //! Create a compile-time string from a string literal.
+    //! @relates hana::basic_string
+    //!
+    //! This macro is a more convenient alternative to `basic_string_c`
+    //! for creating compile-time strings. However, since this macro uses
+    //! a lambda internally, it can't be used in an unevaluated context,
+    //! or where a constant expression is expected before C++17.
+    //!
+    //!
+    //! Example
+    //! -------
+    //! @include example/basic_string/macro.cpp
+#ifdef BOOST_HANA_DOXYGEN_INVOKED
+    auto BOOST_HANA_BASIC_STRING(type, s) = see documentation;
+    #define BOOST_HANA_BASIC_STRING(type, s) see documentation
+
+    // Note:
+    // The trick above seems to exploit a bug in Doxygen, which makes the
+    // BOOST_HANA_STRING macro appear in the related objects of hana::string
+    // (as we want it to).
+#else
+    // defined in <boost/hana/basic_string.hpp>
+#endif
+
+#ifdef BOOST_HANA_CONFIG_ENABLE_BASIC_STRING_UDL
+    namespace literals {
+        //! Creates a compile-time string from a string literal.
+        //! @relatesalso boost::hana::string
+        //!
+        //! The string literal is parsed at compile-time and the result is
+        //! returned as a `hana::string`. This feature is an extension that
+        //! is disabled by default; see below for details.
+        //!
+        //! @note
+        //! Only narrow string literals are supported right now; support for
+        //! fancier types of string literals like wide or UTF-XX might be
+        //! added in the future if there is a demand for it. See [this issue]
+        //! [Hana.issue80] if you need this.
+        //!
+        //! @warning
+        //! This user-defined literal is an extension which requires a special
+        //! string literal operator that is not part of the standard yet.
+        //! That operator is supported by both Clang and GCC, and several
+        //! proposals were made for it to enter C++17. However, since it is
+        //! not standard, it is disabled by default and defining the
+        //! `BOOST_HANA_CONFIG_ENABLE_STRING_UDL` config macro is required
+        //! to get this operator. Hence, if you want to stay safe, just use
+        //! the `BOOST_HANA_STRING` macro instead. If you want to be fast and
+        //! furious (I do), define `BOOST_HANA_CONFIG_ENABLE_STRING_UDL`.
+        //!
+        //!
+        //! Example
+        //! -------
+        //! @include example/string/literal.cpp
+        //!
+        //! [Hana.issue80]: https://github.com/boostorg/hana/issues/80
+        template <typename CharT, CharT ...s>
+        constexpr auto operator"" _s();
+    }
+#endif
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_FWD_BASIC_STRING_HPP

include/boost/hana/fwd/integral_constant.hpp

@@ -69,6 +69,42 @@ BOOST_HANA_NAMESPACE_BEGIN
     constexpr char_<c> char_c{};
 
 
+    //! @relates hana::integral_constant
+    template <wchar_t c>
+    using wchar_ = integral_constant<wchar_t, c>;
+
+    //! @relates hana::integral_constant
+    template <wchar_t c>
+    constexpr wchar_<c> wchar_c{};
+
+
+    //! @relates hana::integral_constant
+    template <char16_t c>
+    using char16_ = integral_constant<char16_t, c>;
+
+    //! @relates hana::integral_constant
+    template <char16_t c>
+    constexpr char16_<c> char16_c{};
+
+
+    //! @relates hana::integral_constant
+    template <char32_t c>
+    using char32_ = integral_constant<char32_t, c>;
+
+    //! @relates hana::integral_constant
+    template <char32_t c>
+    constexpr char32_<c> char32_c{};
+
+
+    //! @relates hana::integral_constant
+    template <typename CharT, CharT c>
+    using basic_char_ = integral_constant<CharT, c>;
+
+    //! @relates hana::integral_constant
+    template <typename CharT, CharT c>
+    constexpr basic_char_<CharT, c> basic_char_c{};
+
+
     //! @relates hana::integral_constant
     template <short i>
     using short_ = integral_constant<short, i>;

include/boost/hana/wstring.hpp

@@ -0,0 +1,33 @@
+/*!
+@file
+Defines `boost::hana::wstring`.
+
+@copyright Louis Dionne 2013-2018
+Distributed under the Boost Software License, Version 1.0.
+(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
+ */
+
+#ifndef BOOST_HANA_WSTRING_HPP
+#define BOOST_HANA_WSTRING_HPP
+
+#include <boost/hana/basic_string.hpp>
+#include <boost/hana/fwd/core/make.hpp>
+#include <boost/hana/fwd/core/to.hpp>
+
+BOOST_HANA_NAMESPACE_BEGIN
+
+template <wchar_t ...s>
+using wstring = basic_string<wchar_t, s...>;
+
+using wstring_tag = basic_string_tag<wchar_t>;
+
+constexpr auto make_wstring = make<wstring_tag>;
+
+constexpr auto to_wstring = to<wstring_tag>;
+
+template <wchar_t ...s>
+constexpr wstring<s...> wstring_c{};
+
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_WSTRING_HPP

test/basic_string/any_of.cpp

@@ -0,0 +1,43 @@
+// Copyright Louis Dionne 2013-2017
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
+
+#include <boost/hana/any_of.hpp>
+#include <boost/hana/assert.hpp>
+#include <boost/hana/basic_string.hpp>
+#include <boost/hana/equal.hpp>
+#include <boost/hana/integral_constant.hpp>
+#include <boost/hana/not.hpp>
+
+#include "test_basic_string.hpp"
+namespace hana = boost::hana;
+
+template <typename C>
+void test() {
+    BOOST_HANA_CONSTANT_CHECK(hana::any_of(
+                                BOOST_HANA_BASIC_STRING(C, "abcd"),
+                                hana::equal.to(hana::basic_char_c<C, CONVERT_C('b')>)
+    ));
+
+    BOOST_HANA_CONSTANT_CHECK(hana::not_(hana::any_of(
+                                           BOOST_HANA_BASIC_STRING(C, ""),
+                                           hana::always(hana::true_c)
+    )));
+
+    BOOST_HANA_CONSTANT_CHECK(hana::not_(hana::any_of(
+                                           BOOST_HANA_BASIC_STRING(C, "abcd"),
+                                           hana::equal.to(hana::basic_char_c<C, CONVERT_C('z')>)
+    )));
+
+    BOOST_HANA_CONSTANT_CHECK(hana::any_of(
+                                BOOST_HANA_BASIC_STRING(C, "abc\x80" "d"),
+                                hana::equal.to(hana::basic_char_c<C, CONVERT_C('\x80')>)
+    ));
+}
+
+int main() {
+  test<char>();
+  test<wchar_t>();
+  test<char16_t>();
+  test<char32_t>();
+}