Create 4.md

Author: gammasoft71

docs/documentation/tips_and_tricks/4.md

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+# xtd::collections::array_list a heterogeneous container supporting multiple types (🟢 Beginner)
+
+How to store any type with a simple xtd collection, and allow them to be easily manipulated.
+
+## Simple example
+
+```cpp
+#include <xtd/xtd>
+
+auto main() -> int {
+  for (auto item : collections::array_list {"42", 42, 42_s, .42}) {
+    console::write("{,-8} --> ", item);
+    if (is<string>(item)) console::write_line("{}", as<string>(item).quoted());
+    else if (is<int>(item)) console::write_line("0x{:X4}", as<int>(item));
+    else if (is<time_span>(item)) console::write_line("{} seconds", as<time_span>(item).seconds());
+    else console::write_line("[{}]", item);
+  }
+}
+```
+
+```cpp
+// This code can produce the following output:
+//
+// 42       --> "42"
+// 42       --> 0x002A
+// 00:00:42 --> 42 seconds
+// 0.42     --> [0.42]
+```
+
+*	[xtd::collections::array_list](https://gammasoft71.github.io/xtd/reference_guides/latest/group__collections.html#ga83a0a06ecb97330626993339079ebbf6) allows you to store any type.
+* The operator [xtd::is](https://gammasoft71.github.io/xtd/reference_guides/latest/group__xtd__core.html#ga0a8b1861b61e1d6371264460d8ee4bc6) easily determines the type of the stored value.
+* The operator [xtd::as](https://gammasoft71.github.io/xtd/reference_guides/latest/group__xtd__core.html#ga9b52c9f607207f23a4f4d2e4bd94eb29) intuitively converts the stored value into the desired type.
+* No macros or hidden tricks — only modern C++.
+
+## Custom types
+
+Yes of course you can store your own type in [xtd::collections::array_list](https://gammasoft71.github.io/xtd/reference_guides/latest/group__collections.html#ga83a0a06ecb97330626993339079ebbf6).
+
+```cpp
+#include <xtd/xtd>
+
+struct foo {
+  int value;
+  
+  bool operator ==(const foo& f) const noexcept {return value == f.value;}
+  bool operator <(const foo& f) const noexcept {return value < f.value;}
+  bool operator >(const foo& f) const noexcept {return value > f.value;}
+};
+
+struct bar : public icomparable<bar>, public iequatable<bar> {
+  bar() = default;
+  bar(int value) : value {value} {}
+  
+  int32 compare_to(const bar& obj) const noexcept override {return value < obj.value ? -1 : value > obj.value ? 1 : 0;}
+  bool equals(const bar& obj) const noexcept override {return value == obj.value;}
+  
+  int value;
+  
+};
+
+auto main() -> int {
+  for (auto item : collections::array_list {"42", 42, 42_s, .42, foo {42}, bar {42}}) {
+    console::write("{,-8} --> ", item);
+    if (is<string>(item)) console::write_line("{}", as<string>(item).quoted());
+    else if (is<int>(item)) console::write_line("0x{:X4}", as<int>(item));
+    else if (is<time_span>(item)) console::write_line("{} seconds", as<time_span>(item).seconds());
+    else if (is<foo>(item)) console::write_line("f{}", as<foo>(item).value);
+    else if (is<bar>(item)) console::write_line("b{}", as<bar>(item).value);
+    else console::write_line("[{}]", item);
+  }
+}
+```
+
+```cpp
+// This code can produce the following output:
+//
+// 42       --> "42"
+// 42       --> 0x002A
+// 00:00:42 --> 42 seconds
+// 0.42     --> [0.42]
+// foo      --> f42
+// bar      --> b42
+```
+
+*	The only constraint is to have to declare at least the following three operators: `==`, `<` and `>` as in the example with the `foo` structure.
+* Or to inherit the interfaces [xtd::icomparable](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1icomparable.html) and [xtd::iequatable](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1iequatable.html) as in the example with the structure `bar`.
+
+## Conclusion
+
+* It has never been easier to store and manipulate a heterogeneous set of elements in a collection than with xtd.
+* In modern C++ we could use a [std::vector<std::any>](https://en.cppreference.com/w/cpp/container/vector.html) but not as easy and as advanced as [xtd::collections::array_list](https://gammasoft71.github.io/xtd/reference_guides/latest/group__collections.html#ga83a0a06ecb97330626993339079ebbf6) does not allow it.
+* [std::variant](https://en.cppreference.com/w/cpp/utility/variant.html) would also be a possibility but it forces you to know the types in advance and with the disadvantage also of being much more verbose.
+* Other libraries / frameworks such as Boost and Qt also allow you to store a set of varied types but not with the simplicity and elegance of [xtd::collections:array_list](https://gammasoft71.github.io/xtd/reference_guides/latest/group__collections.html#ga83a0a06ecb97330626993339079ebbf6).
+
+> **Did you know?**
+>
+> There is also a container [xtd::collections::hash_table](https://gammasoft71.github.io/xtd/reference_guides/latest/group__collections.html#ga5a1cbe0162263e2c6626f996ca032078) which allows as [xtd::collections::array_list](https://gammasoft71.github.io/xtd/reference_guides/latest/group__collections.html#ga83a0a06ecb97330626993339079ebbf6) to manage a collection of heterogeneous types but sorted on a key that can itself be of different types.
+
+## To go further
+
+* [xtd::collections::array_list](https://gammasoft71.github.io/xtd/reference_guides/latest/group__collections.html#ga83a0a06ecb97330626993339079ebbf6) uses a [xtd::any_object](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1any__object.html) to store the different types.
+* [xtd::any_object](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1any__object.html) est utilisé par différents composants de xtd. Comme par example :
+  * [xtd::threading::parameterized_thread_start](https://gammasoft71.github.io/xtd/reference_guides/latest/group__delegates.html#ga1961ded285db6ac6d364694eda5379a3) using by [xtd::threading::thread](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1threading_1_1thread.html) to start a thread with parameter.
+  * [Xtd::forms::control::tag](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1forms_1_1control.html#a688b27af8a0fa5572022c422bcb3eba1) to store a user object, like all other components using the tag.
+
+## See also
+
+* [Tips & Tricks](/docs/documentation/tips_and_tricks)
+* [Documentation](/docs/documentation)