werkzeug::

This is a collection of tools/utilities I wrote over time. Most parts are independent of eachother, some rely on eachother.

It is sort of a general utilities library, but you are unlikely go use every part of it.

"Werkzeug" means "tool" in german, hence the name.

Who is this for?

Primarily me and anybody who is interested. I wrote these things out of curiosity/because they seemed interesting.

Maybe you can take something from it.

How does it work?

While its technically a lot of seperate parts, there are common utilities that are used across many different files.

The library currently provides a simple CMake script allowing its in-tree usage, but no installation utilities.

Interesting things in here:

• Expected: A slightly improved alternative to std::expected
• inheritance_variant: A variant-like sum type
• overload: A tool to easily create overloads from multiple callables
• aggregate_ordering: Utility to ad-hoc create a complex ordering relation, e.g. for use in sorting algorithms
• type_pack, value_pack: Wrappers to enable easy handling of parameter packs
• type_traits: A large wrapper for many type traits
• Callable_Wrapper: A wrapper to allow passing C++ callables to C-APIs
• explicit_: A wrapper that disallows implicit conversions
• select_overload': Utility to select a specific overload form an overload set
• try_constexpr_invoke: Utility to potentially evaluate a function at compile time
• State_Machine: Utility to create simple state machines
• Nd array types: Nd linearly indexed arrays/tables (similar to C++23 std::mdarray). Multiple versions with different axis settings, as well as interpolating versions exist.

Overview:

The container/ and memory/ parts are mainly rewrites of existing (standard library) tools for exploration/technical learning purposes. The things in simple_vector_implementation/ are iterative, simpler versions of vector. They mostly exist for learners to look at with less "feature related clutter". A complete and advanced vector implementation is in container/dynamic_array.hpp.

Note that not everything in here is of similar implementation quality/completeness. Some things are as complete as can be with correct noexcept specifiers, others may lack all basic functionality.

This is an overview of all the seperate files and their contents:

For additional examples you can look at the tests/ (if they exist...)

Callable_Wrapper

This exists to easiy create wrappers allowing using a generic C++ callable with a C language API that accepts a void* for any user data.

This is mostly useful when wanting to use established C libraries in C++ code. A prime example would be GNU scientific libraries.

Example:

// some C API.In this example it just invokes our function
double c_api_mid( double a, double b, double(*f)(double a, void* ud, double b), void* ud )
{
	return f(a,ud,b);
}

// Your C++ callable. Capture only to make it non-trivial to convert to a function pointer.
constexpr auto callable = [&]( double a, double b )
{
	return a+b;
};

// create the callable wrapper
auto wrapper = werkzeug::make_wrapper<double(double,double,user_data)>( callable );
// calling the C API gives us the exact same value as calling
REQUIRE( callable(0,1) == c_api_tail( 0, 1, wrapper, &wrapper ) );

Expected

This is an extended version of std::expected. Notably it allows you to directly specifc multiple error types (instead of having to manually interact with a variant).

Its monadic interface automatically transforms values and transfers errors along.

Example:

enum class err_a { a1 }; // some error codes for demo purposes. Could also be any other type.

enum class err_b { b1 };

Expected<int,err_a> expected_a = 0; // expected now contains an int
Expected<int,err_a> expected_b = err_a::a1; // expected now contains an err_a

{ // using monadic interface transforming the result
	constexpr auto transform = []( int i ) -> long
	{
		return i;
	}

	Expected<long,err_a> res_a = expected_a.and_then( transform ); // res_a now contains the long 0

	Expected<long,err_a> res_b = expected_b.and_then( transform ); // res_a now contains the err_a
}

{
	constexpr auto transform_to_expected( int i ) -> Expected<long,err_b> 
	{
		if ( i == 0 )
		{
			return i;
		}
		else
		{
			return err_b::b1;
		}
	}

	Expected<long,err_a,err_b> res_a = expected_a.and_then( transform_to_expected ); // res_a now contains the long 0

	expected_a.emplace( 1 ); // changes the value in `expected_a` to 1
	Expected<long,err_a,err_b> res_a2 = expected_a.and_then( transform_to_expected ); // res_a2 now contains err_b::b1

	Expected<long,err_a,err_b> res_b = expected_b.and_then( transform_to_expected ); // res_b now contains err_a::a1
}

explicit_

A helper type that does not allow implicit conversions

inheritance_variant

This is a variant-like sum type that only allows storage of a compile time known list of types derived from a common Base. It provieds access to a base pointer, allowing for slightly cleaner usage without having to go through std::visit.

It does not require a virtual destructor. The objects are stored within the variant and destroyed according to their index.

The provided API is largely identical to that of std::variant

Example:

enum class type
{
	base, derived
};


struct Base
{
	virtual type type_id() const
	{
		return type::base;
	}

	// no virtual destructor required for the usage
};

struct Derived : Base
{
	virtual type type_id() const override
	{
		return type::derived;
	}
};

using variant_t = werkzeug::inheritance_variant<Base, Derived>;

variant_t var{ Base{} };
REQUIRE( var->type_id() == type::base );

var.emplace<Derived>();
REQUIRE( var->type_id() == type::derived );

overload

This is an extension upon the classic pattern

template<typename...Ts>
struct overload : Ts...
{
	using Ts::operator() ...;
};

Notably this overload also takes both member function and member data pointers, allowing a usage similar to std::invoke, but with less overhead:

Example:

struct A
{
	int f();
};

struct B
{
	int i = 0;
};

constexpr overload my_overload = {
	&A::f,
	&B::i,
}

int a = my_overload(A{}); // invokes A::f
int b = my_overload(B{}); // accesses and returns B::i

If the provided projectors do not have a common return type, the return type of overload::operator() will be void and potential results will be discarded.

select_overload

This is a helper to select a selecfic signature from an overload set.

Example:

int f( int );
void f( double );

constexpr auto f_int = select_overload<int>( &f );

parameter_pack

This header contains utilities for dealing with parameter packs. For this it primarily uses type_pack<Ts...> and value_pack<auto...>.

Both provide the same functionalities:

List of provided utilities:

• type_pack_c<T>: concept to check whether T is an instantiation of type_pack
• value_pack_c<T>: concept to check whether T is an instantiation of value_pack
• pack::size: static member containing the size of the pack
• pack::contains<X>(): static member returning whether pack contains X (type or value)
• pack::index_of<X>(): static member returning the index of X in pack
• type_pack::type_at<I>: static member typedef, giving the type at index I
• value_pack::value_at<I>: static data member, giving the value at index I
• type_at_index<I,type_pack>: freestanding metafunction get thet type at I. Can also be used as type_at_index<I,Ts...>.
• value_at_index<I,valze_pack>: freestanding metafunction to get the value at index I. Can also be used as value_at_index<I,Vs...>
• all_unique<Ts...>, all_unique<type_pack>, all_unique<value_pack>: freestanding metafunction to querry if all elements in a pack are unique.
• pack_inclues<pack1,pack2>: freestanding metafunction to check whether pack1 fully includes pack2
• append<pack1,X>: freestanding metafunction that appends X to pack1. Can also be used as append<pack1,pack2> to append the entire pack
• append_if_unique<pack1,X>: freestanding metafunction that appends X to pack1, if pack1 does not already contain X
• static_for<pack>( Callable&& callable ): function that invokes Callable for every type or value in pack, passing it as a distinct type, so it can be used as a constant expression

State_Machine

This provides a utility to create a rudimentary state machine from an enum and functions.

Example:

// an enum for our states
enum class states : unsigned char
{
    A, B
};


// the machine itself
struct Flip_Flop_Machine
    : werkzeug::State_Machine<states,2,Flip_Flop_Machine>
{
	// some custom members
    int i = 0;

    using Base = werkzeug::State_Machine<states,2,Flip_Flop_Machine>;

	// just a default ctor
    constexpr Flip_Flop_Machine()
        : Base{ states::A }
    { };

	// declare the state function template.
    template<states>
    states func_for() = delete; //delete its default. That means that the compiler catches if we have not implemented all of them
};

// implement the state function for states::A
template<>
states Flip_Flop_Machine::func_for<states::A>()
{
    std::cout << "FLIP\n";
    ++i;
    return states::B; // returns the next state we want to go to.
}

// implement the state function for states::B
template<>
states Flip_Flop_Machine::func_for<states::B>()
{
    std::cout << "flop\n";
    ++i;
    return states::A; // returns the next state we want to go to.
}

int main()
{
	Flip_Flop_Machine m;

	m.execute_active() // prints "FLIP"
	m.execute_active() // prints "flop"

	REQUIRE( m.i == 2 );
}

type_traits

This header provides a generic type trait type_traits<T>, that contains almost all information about a type.

For every operation, there is named member type trait, that tells you if the operation is possible, trivial or nothrow.

Examples

• traits<T>::default_construct::possible
• traits<T>::swap::nothrow
• traits<T>::copy_construct::trivial
• traits<T>::template invocable<Args...>::possible
• traits<T>::subscript::nothrow

All member traits follow the pattern of providing possible, trivial and nothrow to check the respective property.

type_constant

Pretty much std::integral_constant with a better name.

Provides a user defined literal _tc that automatically creates a size_t or long double type_constant:

constexpr auto A = 0_tc; // type_constant<0,size_t>{}
constexpr auto B = 0.0_tc; // type_constant<0.0l,long double>{}

type_erased_object

An exploration into creating a type erased wrapper that provides specifications for an interface.

struct S
{ 
	int i;
};

std::ostream& operator<<( std::ostream& os, const S& s )
{
	return os << s.i;
}

std::stream& operator>>( std::istream& is, const S& s )
{
	return is >> s.i;
}

Shared_Object obj{ S, Generic_Stream_Extraction<S>{}, Generic_Stream_Insertion<S>{} }; // create an erased object with its set of supported operations

std::string_stream ss("42");
obj.operation<Stream_Extraction>()(ss); // `Stream_Extraction` is a predefined interface that is implemented by the `Generic_Stream_Extraction<T>`

obj.operation<Stream_Insertion>()(std::cout); // prints 42


if ( auto op_ptr = obj.try_operation<Unsupported_Operation>() )
{
	// never happens, because no `Unsupported_Operation` was provided.
}
if ( auto op_ptr = obj.try_operation<Stream_Insertion>() )
{
	(*ptr)( std::cout ); // prints 42 again
}

try_constexpr_invoke

This utility will try to invoke a callable at compile time. If that is possible, it provides the value. Otherwise it does not.

constexpr int yes()
{ return 0; }

constexpr auto result = try_constexpr_invoke( yes );

static_assert( result.has_value() );
static_assert( result.value() == 0 );

int no()
{ return 0; }

constexpr auto result = try_constexpr_invoke( no );

static_assert( not result.has_value() );

aggregate_ordering

This is a fancy little utility that easily lets you create custom ordering ad-hoc

// some data structure
struct S
{
	int i;
	int j;
	double d;
};

constexpr auto ordering = aggregate_ordering{  // sort by
	by{ &S::i, less{} }, 	// ascending i first
	by{ &S::d, less{} },	// ascending d next
	by{ &S::j, greater{} } 	// descending j last
};

S arr[] = {
	{ .i = 0, .j= 1, .d=2.0 },
	{ .i = 2, .j= 2, .d=3.0 },
	{ .i = 2, .j= 2, .d=2.0 },
	{ .i = 0, .j= 3, .d=2.0 },
	{ .i = 3, .j= 4, .d=2.0 }
};

std::ranges::stable_sort( arr, ordering );

REQUIRE( arr[0].i == 3 );

REQUIRE( arr[1].i == 2 );
REQUIRE( arr[1].d == 3.0 );

REQUIRE( arr[2].i == 2 );
REQUIRE( arr[2].d == 2.0 );

REQUIRE( arr[3].j == 1 );

Nd_Array

These array types are similar to std::mdarray, but are C++17 compatible. Their primary purpose is the implementation of the Interpolating_ table types.

• Array_ND is simply an ND array, supporting indexing via operator()
• Bounded_Array_Nd also has lower and upper bounds attachted to each axis
• Axis_Tick_Array_Nd instead has ticks for every dimension saved, meaning they can be non-linearly/logarythmically spaced.
• Basic_Interpolating_Array_Nd is a Bounded_Array_Nd that can interpolate at an arbitrary position in the hypercube, or do simple extrapolation outside of it.
• Advanced_Interpolating_Array_Nd is an Axist_Tick_Array_Nd that supports interpolation.

Notable features:

• All of them also provide a member function make_view() that creats a std::span like object to view the array/table. These objects support the exact same functionalities as the owning array itself.
• These types can be saved to an std::ostream and constructed from an std::ostream
• Interpolation works in N dimensions, either as lin, log or linlog interpolation.

The internal data structre is as follows:

Array_Nd:
[ axis lengths ] [ data ]

Bounded_Array_Nd
[ Array_Nd ] [ axis_lower_bounds ] [ axis_upper_bounds ] [ axis_is_log ]

Basic_Interpolating_Table
[ Bounded_Array_Nd ]

Axis_Tick_Array_Nd
[ Array_Nd ] [ axis_ticks ]

[ Advanced_Interpolating_Table ]
[ Axis_Tick_Array_Nd ]

Achknowledgements

• The tests use doctest under the MIT license