[feature] radr::istream

Author: h-2

docs/implementation_status.md

@@ -51,6 +51,7 @@ All range adaptors from this library are available in C++20, although `radr::as_
 | Range factories               | Equivalent in `std::`   | Remarks                                              |
 |-------------------------------|-------------------------|------------------------------------------------------|
 | `radr::empty<T>`              | `std::views::empty`     |                                                      |
+| `radr::istream<Val>`          | `std::views::istream`   |                                                      |
 | `radr::repeat(val, bound)`    | `std::views::repeat`    | allows indirect storage and static bounds            |
 | `radr::single(val)`           | `std::views::single`    | allows indirect storage                              |
 

include/radr/factory/istream.hpp

@@ -0,0 +1,58 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// Copyright (c) 2023-2025 Hannes Hauswedell
+//
+// Licensed under the Apache License v2.0 with LLVM Exceptions.
+// See the LICENSE file for details.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#pragma once
+
+#include <istream>
+
+#include "radr/generator.hpp"
+
+namespace radr::detail
+{
+
+template <class Val, class CharT, class Traits>
+concept stream_extractable = requires(std::basic_istream<CharT, Traits> & is, Val & t) { is >> t; };
+
+}
+
+namespace radr
+{
+
+/*!\brief A range factory that produces a range over the values from an istream.
+ * \tparam Val The type to extract into.
+ * \tparam CharT The character type of the stream.
+ * \tparam Traits CharTraits of the stream.
+ * \param[in,out] stream The stream to extract from.
+ * \details
+ *
+ * Values are extracted from the stream as if by `stream >> val;`.
+ *
+ * The returned range is a specialisation of radr::generator, i.e. it is always a move-only, single-pass range.
+ *
+ */
+template <typename Val, class CharT = char, class Traits = std::char_traits<CharT>>
+generator<Val &, Val> istream(std::basic_istream<CharT, Traits> & stream)
+{
+    static_assert(std::movable<Val>, "The constraints for the Val type of radr::istream were not met.");
+    static_assert(detail::stream_extractable<Val, CharT, Traits>,
+                  "The Val type cannot be extracted from the stream passed to radr::istream.");
+
+    Val value;
+    stream >> value;
+
+    while (stream)
+    {
+        co_yield value;
+        stream >> value;
+    }
+}
+
+} // namespace radr

tests/unit/factory/CMakeLists.txt

@@ -1,3 +1,4 @@
 radr_unit_test(empty)
+radr_unit_test(istream)
 radr_unit_test(single)
 radr_unit_test(repeat)

tests/unit/factory/istream.cpp

@@ -0,0 +1,59 @@
+#include <sstream>
+#include <string>
+#include <vector>
+
+#include <gtest/gtest.h>
+#include <radr/test/gtest_helpers.hpp>
+
+#include <radr/factory/istream.hpp>
+
+TEST(ViewsIstreamConceptsTest, ConceptValidation)
+{
+    std::istringstream input("1 2 3");
+    auto               view = radr::istream<int>(input);
+
+    // Checking the relevant concepts
+    EXPECT_TRUE(std::ranges::input_range<decltype(view)>);
+    EXPECT_TRUE(std::ranges::view<decltype(view)>);
+    EXPECT_TRUE(std::is_move_constructible_v<decltype(view)>);
+    EXPECT_FALSE(std::ranges::common_range<decltype(view)>);
+    EXPECT_FALSE(std::ranges::sized_range<decltype(view)>);
+    EXPECT_FALSE(std::ranges::contiguous_range<decltype(view)>);
+    EXPECT_FALSE(std::is_default_constructible_v<decltype(view)>);
+    EXPECT_FALSE(std::ranges::random_access_range<decltype(view)>);
+}
+
+TEST(istream, EmptyInput)
+{
+    std::istringstream input("");
+    auto               view = radr::istream<int>(input);
+    EXPECT_TRUE(view.begin() == view.end());
+}
+
+TEST(istream, ReadIntegers)
+{
+    std::istringstream input("10 20 30");
+    auto               view = radr::istream<int>(input);
+    EXPECT_RANGE_EQ(view, (std::vector<int>{10, 20, 30}));
+}
+
+TEST(istream, ReadStrings)
+{
+    std::istringstream input("hello world test");
+    auto               view = radr::istream<std::string>(input);
+    EXPECT_RANGE_EQ(view, (std::vector<std::string>{"hello", "world", "test"}));
+}
+
+TEST(istream, StopOnMalformedData)
+{
+    std::istringstream input("42 invalid 84");
+    auto               view = radr::istream<int>(input);
+    EXPECT_RANGE_EQ(view, (std::vector<int>{42}));
+}
+
+TEST(istream, ReadChars)
+{
+    std::istringstream input("hello world test");
+    auto               view = radr::istream<char>(input);
+    EXPECT_RANGE_EQ(view, std::string{"helloworldtest"});
+}