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https://github.com/dice-group/dice-template-library

This template library is a collection of template-oriented code that we, the Data Science Group at UPB, found pretty handy.
https://github.com/dice-group/dice-template-library

cpp20 switch-case template tuple

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This template library is a collection of template-oriented code that we, the Data Science Group at UPB, found pretty handy.

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# Dice Template Library



This template library is a collection of template-oriented code that we, the Data Science Group at UPB, found pretty

handy.

It contains:



- `switch_cases`: Use runtime values in compile-time context.

- `integral_template_tuple`: Create a tuple-like structure that instantiates a template for a range of values.

- `integral_template_variant`: A wrapper type for `std::variant` guarantees to only contain variants of the form `T` where $\texttt{ix}\in [\texttt{first},\texttt{last}]$ (inclusive).

- `for_{types,values,range}`: Compile time for loops for types, values or ranges

- `polymorphic_allocator`: Like `std::pmr::polymorphic_allocator` but with static dispatch

- `limit_allocator`: Allocator wrapper that limits the amount of memory that is allowed to be allocated

- `DICE_MEMFN`: Macro to pass member functions like free functions as argument. 

- `pool` & `pool_allocator`: Arena/pool allocator optimized for a limited number of known allocation sizes.

- `DICE_DEFER`/`DICE_DEFER_TO_SUCCES`/`DICE_DEFER_TO_FAIL`: On-the-fly RAII for types that do not support it natively (similar to go's `defer` keyword)

- `overloaded` and `match`: Batteries for `std::variant` (and also `dtl::variant2`. Compose re-usable visitors with `overload` or apply a single-use visitor directly with `match`.

- `flex_array`: A combination of `std::array`, `std::span` and a `vector` with small buffer optimization

- `tuple_algorithms`: Some algorithms for iterating tuples

- `fmt_join`: A helper to join elements of a range with a separator for use with `std::format` alike [fmt::join](https://fmt.dev/latest/api/#range-and-tuple-formatting)

- `generator`: The reference implementation of `std::generator` from [P2502R2](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2502r2.pdf)

- `channel`: A single producer, single consumer queue

- `variant2`: Like `std::variant` but optimized for exactly two types

- `mutex`/`shared_mutex`: Rust inspired mutex interfaces that hold their data instead of living next to it

- `static_string`: A string type that is smaller than `std::string` for use cases where you do not need to resize the string

- `ranges`: Additional range algorithms and adaptors that are missing from the standard library.  



## Usage



### `switch_cases`



Use runtime values in compile-time context. This is realised by instantiating ranges of values at compile-time and

dispatching to the correct version at runtime. You can add fallbacks for when the runtime value lies outside the range

defined. By using `switch_cases` inside of `switch_cases` multidimensional ranges can be handled as well. Examples can

be found [here](examples/examples_switch_cases.cpp).



### `integral_template_tuple`



Create a tuple-like structure that instantiates a template for a range of values. Let's say you have a type like



```cpp

template  struct my_type{...};

```



Then you can create a tuple consisting of `my_type, my_type, ...` up to `my_type` for `i<=j` with this code.

Negative indices, recasting to fewer values and non-default construction is also possible. Examples can be

found [here](examples/examples_integral_template_tuple.cpp).



### `integral_template_variant`



Creates a variant-like structure that instantiates a template for a range of values. Let's say you have a type like

```cpp

template  struct my_type{...};

```



Then you can create a variant consisting of `my_type, my_type, ..., my_type` with the help of `integral_template_variant`.

Negative indices, and j <= i are also possible. Examples can be

found [here](examples/examples_integral_template_variant.cpp).



### `for_{types,values,range}`



Different flavors of compile time loops that allow to iterate types, values or ranges at compile time. Types and values are provided as template arguments and a lambda to be called for each of them is passed as function argument, e.g. `for_types([]() {})` and `for_values<1, 1.1, 'c'>([](auto x) {})`. Ranges are defined by template parameters for start and exclusive end and receive a function to be applied to each range element as function argument, e.g. `for_range<3, 5>([](auto x) {})`, including support for decreasing ranges and negative indices, e.g. `for_range<2, -4>([](auto x) {})`. Examples can

be found [here](examples/examples_for.cpp).



### `polymorphic_allocator`

A `std::pmr::polymorphic_allocator`-like type that uses static dispatch instead of dynamic dispatch to choose the allocator.

This allocator is primarily useful for situations where you have inhomogeneous memory and one of the memory

types does not allow dynamic dispatch using vtables; but you still want to mix and match values from both memory types.



For example, you might have some allocations in persistent or shared memory (or generally: memory-mapped allocations) and others on the heap.

The problem with `mmap` allocations is that they will be placed at an arbitrary position in virtual memory each time they are loaded,

therefore absolute pointers will cause segfaults if the segment is reloaded.

Which means: vtables will not work (because they use absolute pointers) and therefore you cannot use `std::pmr::polymorphic_allocator`.



### `limit_allocator`

Allocator wrapper that limits the amount of memory that can be allocated through the inner allocator.

If the limit is exceeded it will throw `std::bad_alloc`.



### `DICE_MEMFN`

DICE_MEMFN is a convenience macro that makes it easy to pass member functions as argument, e.g., to range adaptors.

It eliminates boilerplate code by creating a lambda that captures this and perfectly forwards

arguments to your member function.



### `pool_allocator`

A memory arena/pool allocator with configurable allocation sizes. This is implemented

as a collection of pools with varying allocation sizes. Allocations that do not

fit into any of its pools are directly served via `new`.



### `DICE_DEFER`/`DICE_DEFER_TO_SUCCES`/`DICE_DEFER_TO_FAIL`

A mechanism similar to go's `defer` keyword, which can be used to defer some action to scope exit.

The primary use-case for this is on-the-fly RAII-like resource management for types that do not support RAII (for example C types).

Usage examples can be found [here](examples/examples_defer.cpp).



### `tuple algorithms`

Some algorithms for iterating tuples, for example `tuple_fold` a fold/reduce implementation for tuples.



### `fmt_join`

Works just like [`fmt::join`](https://fmt.dev/latest/api/#range-and-tuple-formatting) but for `std::format`.



### `flex_array`

A combination of `std::array`, `std::span` and a `vector` with small buffer optimization where the size is either

statically known or a runtime variable depending on the `extent`/`max_extent` template parameters



### `generator`

The reference implementation of `std::generator` from [P2502R2](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2502r2.pdf).

By default, the generator and corresponding utilities are exported under the `dice::template_library::` namespace.

If you want this generator to serve as a drop in replacement for `std::generator` until it arrives

use `#define DICE_TEMPLATELIBRARY_GENERATOR_STD_COMPAT 1` before including the generator header. That will export

all generator related things under namespace `std::`.



### `channel`

A single producer, single consume queue. This can be used to communicate between threads in a more high level

fashion than a mutex+container would allow.



### `variant2`

Like `std::variant` but specifically optimized for usage with two types/variants. 

The internal representation is a `union` of the two types plus a 1 byte (3 state) discriminant.

Additionally, `visit` does not involve any virtual function calls.



### `overload` / `match`

Things that are missing around `std::variant` and visitors in the standard library. Implementation of the common `overload` pattern to create re-usable visitors. Also, comes with a `match` function that allows you to declare the visitor directly  inline when applying it. 



### `type_traits.hpp`

Things that are missing in the standard library `` header.



### `mutex`/`shared_mutex`

Rust inspired mutex interfaces that hold their data instead of living next to it.

The benefit of this approach is that it makes it harder (impossible in rust) to access the

data without holding the mutex.



### `static_string`

A string type that is smaller than `std::string` but does not have the ability to grow or shrink.

This is useful if you never need to resize the string and want to keep the memory footprint low.

It also supports allocators with "fancy" pointers.



### `ranges`

Additional range algorithms (e.g. `unique_view`) and adaptors (e.g. a pipeable `all_of`)

that are missing from the standard library.



### Further Examples



Compilable code examples can be found in [examples](./examples). The example build requires the cmake

option `-DBUILD_EXAMPLES=ON` to be added.



## Requirements



A C++20 compatible compiler. Code was only tested on x86_64.



## Include it into your projects



### CMake



add



```cmake

FetchContent_Declare(

        dice-template-library

        GIT_REPOSITORY "https://github.com/dice-group/dice-template-library.git"

        GIT_TAG v1.9.1

        GIT_SHALLOW TRUE)



FetchContent_MakeAvailable(dice-template-library)

```



to your CMakeLists.txt



You can now add it to your target with:



```cmake

target_link_libraries(your_target

        dice-template-library::dice-template-library

        )

```



### conan



You can use it with [conan](https://conan.io/).

To do so, you need to add `dice-template-library/1.9.1` to the `[requires]` section of your conan file.



## Build and Run Tests and Examples



```shell

# get it 

git clone https://github.com/dice-group/dice-template-library.git

cd dice-template-library

# build it

mkdir build

cd build

cmake -DBUILD_TESTING=ON -DBUILD_EXAMPLES=ON ..

make -j$(nproc)

# run tests

make run_tests

# run examples

./examples/examples_integral_template_tuple

./examples/examples_switch_cases

```