Add xtd::linq::enumerable examples and documentation

examples/xtd.core.examples/README.md

@@ -282,6 +282,8 @@
 * [enumerable_count](linq/enumerable_count/README.md) shows how to use [xtd::linq::enumerable::count](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1linq_1_1enumerable.html#ae8deab4a1605619cb40cd56504a5b54c) method.
 * [enumerable_count2](linq/enumerable_count2/README.md) shows how to use [xtd::linq::enumerable::count](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1linq_1_1enumerable.html#ad9b2c99b2315f698741d2f45b0d4db92) method.
 * [enumerable_count_by](linq/enumerable_count_by/README.md) shows how to use [xtd::linq::enumerable::count_by](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1linq_1_1enumerable.html#a6cda69ae32d618aa9d31e18133861f45) method.
+* [enumerable_default_if_empty](linq/enumerable_default_if_empty/README.md) shows how to use [xtd::linq::enumerable::default_if_empty](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1linq_1_1enumerable.html#a89cb4c7f69e1af47e2d24c5e4e963925) method.
+* [enumerable_default_if_empty2](linq/enumerable_default_if_empty2/README.md) shows how to use [xtd::linq::enumerable::default_if_empty](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1linq_1_1enumerable.html#a77cd5c4f6280710bd7422cb5bb6ca0d1) method.
 * [enumerable_range](linq/enumerable_range/README.md) shows how to use [xtd::linq::enumerable::range](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1linq_1_1enumerable.html#a2ad0f9812852378c4ed08a50f39396cd) method.
 * [enumerable_select](linq/enumerable_select/README.md) shows how to use [xtd::linq::enumerable::select](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1linq_1_1enumerable.html#ae2df9541f109773859bcaaf42015b8cd) method.
 * [enumerable_select2](linq/enumerable_select2/README.md) shows how to use [xtd::linq::enumerable::select](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1linq_1_1enumerable.html#ae2df9541f109773859bcaaf42015b8cd) method.

examples/xtd.core.examples/linq/CMakeLists.txt

@@ -21,6 +21,8 @@ add_projects(
   enumerable_count
   enumerable_count2
   enumerable_count_by
+  enumerable_default_if_empty
+  enumerable_default_if_empty2
   enumerable_range
   enumerable_select
   enumerable_select2

examples/xtd.core.examples/linq/README.md

@@ -19,6 +19,8 @@
 * [enumerable_count](enumerable_count/README.md) shows how to use [xtd::linq::enumerable::count](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1linq_1_1enumerable.html#ae8deab4a1605619cb40cd56504a5b54c) method.
 * [enumerable_count2](enumerable_count2/README.md) shows how to use [xtd::linq::enumerable::count](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1linq_1_1enumerable.html#ad9b2c99b2315f698741d2f45b0d4db92) method.
 * [enumerable_count_by](enumerable_count_by/README.md) shows how to use [xtd::linq::enumerable::count_by](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1linq_1_1enumerable.html#a6cda69ae32d618aa9d31e18133861f45) method.
+* [enumerable_default_if_empty](enumerable_default_if_empty/README.md) shows how to use [xtd::linq::enumerable::default_if_empty](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1linq_1_1enumerable.html#a89cb4c7f69e1af47e2d24c5e4e963925) method.
+* [enumerable_default_if_empty2](enumerable_default_if_empty2/README.md) shows how to use [xtd::linq::enumerable::default_if_empty](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1linq_1_1enumerable.html#a77cd5c4f6280710bd7422cb5bb6ca0d1) method.
 * [enumerable_range](enumerable_range/README.md) shows how to use [xtd::linq::enumerable::range](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1linq_1_1enumerable.html#a2ad0f9812852378c4ed08a50f39396cd) method.
 * [enumerable_select](enumerable_select/README.md) shows how to use [xtd::linq::enumerable::select](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1linq_1_1enumerable.html#ae2df9541f109773859bcaaf42015b8cd) method.
 * [enumerable_select2](enumerable_select2/README.md) shows how to use [xtd::linq::enumerable::select](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1linq_1_1enumerable.html#ae2df9541f109773859bcaaf42015b8cd) method.

examples/xtd.core.examples/linq/enumerable_count/src/enumerable_count.cpp

@@ -1,7 +1,6 @@
 #include <xtd/xtd>
 
 using namespace xtd;
-using namespace xtd::collections::generic;
 
 auto main() -> int {
   auto fruits = array {"apple", "banana", "mango", "orange", "passionfruit", "grape"};

examples/xtd.core.examples/linq/enumerable_default_if_empty/CMakeLists.txt

@@ -0,0 +1,6 @@
+cmake_minimum_required(VERSION 3.20)
+
+project(enumerable_default_if_empty)
+find_package(xtd REQUIRED)
+add_sources(README.md src/enumerable_default_if_empty.cpp)
+target_type(CONSOLE_APPLICATION)

examples/xtd.core.examples/linq/enumerable_default_if_empty/README.md

@@ -0,0 +1,28 @@
+# enumerable_default_if_empty
+
+Shows how to use [xtd::linq::enumerable::default_if_empty](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1linq_1_1enumerable.html#a89cb4c7f69e1af47e2d24c5e4e963925) method.
+
+## Sources
+
+[src/enumerable_default_if_empty.cpp](src/enumerable_default_if_empty.cpp)
+
+[CMakeLists.txt](CMakeLists.txt)
+
+## Build and run
+
+Open "Command Prompt" or "Terminal". Navigate to the folder that contains the project and type the following:
+
+```cmake
+xtdc run
+```
+
+## Output
+
+```
+pet {name=Barley, age=8}
+pet {name=Boots, age=4}
+pet {name=Whiskers, age=1}
+
+pet {name=, age=0}
+
+```

examples/xtd.core.examples/linq/enumerable_default_if_empty/src/enumerable_default_if_empty.cpp

@@ -0,0 +1,37 @@
+#include <xtd/xtd>
+
+using namespace xtd;
+
+struct pet {
+  string name;
+  int age = 0;
+
+  friend bool operator==(const pet& lhs, const pet& rhs) noexcept {
+    return lhs.name == rhs.name && lhs.age == rhs.age;
+  }
+};
+
+auto main() -> int {
+  auto pets1 = array<pet> {
+    {.name = "Barley", .age = 8},
+    {.name = "Boots", .age = 4},
+    {.name = "Whiskers", .age = 1}
+  };
+  for (const auto& [name, age] : pets1.default_if_empty())
+    console::write_line("pet {{name={}, age={}}}", name, age);
+  console::write_line();
+
+  auto pets2 = array<pet> {};
+  for (const auto& [name, age] : pets2.default_if_empty())
+    console::write_line("pet {{name={}, age={}}}", name, age);
+  console::write_line();
+}
+
+// This code produces the following output :
+//
+// pet {name=Barley, age=8}
+// pet {name=Boots, age=4}
+// pet {name=Whiskers, age=1}
+//
+// pet {name=, age=0}
+//

examples/xtd.core.examples/linq/enumerable_default_if_empty2/CMakeLists.txt

@@ -0,0 +1,6 @@
+cmake_minimum_required(VERSION 3.20)
+
+project(enumerable_default_if_empty2)
+find_package(xtd REQUIRED)
+add_sources(README.md src/enumerable_default_if_empty2.cpp)
+target_type(CONSOLE_APPLICATION)

examples/xtd.core.examples/linq/enumerable_default_if_empty2/README.md

@@ -0,0 +1,28 @@
+# enumerable_default_if_empty2
+
+Shows how to use [xtd::linq::enumerable::default_if_empty](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1linq_1_1enumerable.html#a77cd5c4f6280710bd7422cb5bb6ca0d1) method.
+
+## Sources
+
+[src/enumerable_default_if_empty2.cpp](src/enumerable_default_if_empty2.cpp)
+
+[CMakeLists.txt](CMakeLists.txt)
+
+## Build and run
+
+Open "Command Prompt" or "Terminal". Navigate to the folder that contains the project and type the following:
+
+```cmake
+xtdc run
+```
+
+## Output
+
+```
+pet {name=Barley, age=8}
+pet {name=Boots, age=4}
+pet {name=Whiskers, age=1}
+
+pet {name=Default pet, age=0}
+
+```

examples/xtd.core.examples/linq/enumerable_default_if_empty2/src/enumerable_default_if_empty2.cpp

@@ -0,0 +1,41 @@
+#include <xtd/xtd>
+
+using namespace xtd;
+
+struct pet {
+  string name;
+  int age = 0;
+
+  static pet default_pet;
+
+  friend bool operator==(const pet& lhs, const pet& rhs) noexcept {
+    return lhs.name == rhs.name && lhs.age == rhs.age;
+  }
+};
+
+pet pet::default_pet {.name = "Default pet", .age = 0};
+
+auto main() -> int {
+  auto pets1 = array<pet> {
+    {.name = "Barley", .age = 8},
+    {.name = "Boots", .age = 4},
+    {.name = "Whiskers", .age = 1}
+  };
+  for (const auto& [name, age] : pets1.default_if_empty(pet::default_pet))
+    console::write_line("pet {{name={}, age={}}}", name, age);
+  console::write_line();
+
+  auto pets2 = array<pet> {};
+  for (const auto& [name, age] : pets2.default_if_empty(pet::default_pet))
+    console::write_line("pet {{name={}, age={}}}", name, age);
+  console::write_line();
+}
+
+// This code produces the following output :
+//
+// pet {name=Barley, age=8}
+// pet {name=Boots, age=4}
+// pet {name=Whiskers, age=1}
+//
+// pet {name=Default pet, age=0}
+//

src/xtd.core/include/xtd/linq/enumerable.hpp

@@ -494,6 +494,9 @@ namespace xtd {
       /// @tparam source_t The type of the elements of source.
       /// @param source The sequence to return a default value for if it is empty.
       /// @return An xtd::collection::generic::ienumerable <type_t> that contains default_value if source is empty; otherwise, source.
+      /// @par Examples
+      /// The following code example demonstrates how to use xtd::linq::enumerable::default_if_empty <source_t>(const ienumerable <source_t>&) to return a default value if a sequence is empty.
+      /// @include enumerable_default_if_empty.cpp
       template <typename source_t>
       static const ienumerable<source_t>& default_if_empty(const ienumerable<source_t>& source) noexcept {
         return default_if_empty(source, source_t {});
@@ -504,6 +507,9 @@ namespace xtd {
       /// @param source The sequence to return a default value for if it is empty.
       /// @param default_value The value to return if the sequence is empty.
       /// @return An xtd::collection::generic::ienumerable <type_t> that contains default_value if source is empty; otherwise, source.
+      /// @par Examples
+      /// The following code example demonstrates how to use xtd::linq::enumerable::default_if_empty <source_t>(const ienumerable <source_t>&, const source_t&) to return a default value if a sequence is empty.
+      /// @include enumerable_default_if_empty2.cpp
       template <typename source_t>
       static const ienumerable<source_t>& default_if_empty(const ienumerable<source_t>& source, const source_t& default_value) noexcept {
         static thread_local auto result = enumerable_collection<source_t> {};