4_function

Store definition

// SPDX-FileCopyrightText: 2020-2023 Jochem Rutgers
//
// SPDX-License-Identifier: CC0-1.0

// All previous examples had normal variables, which do not have side effects
// when read or written. If a side effect is required, one can define a
// function.  For this, surround the type with ( and ). Read it as a function
// that has an argument of the given type. Functions can be an array, but
// cannot have an initializer.

// The side effect is to be defined in your application. See main.cpp.

(uint64) time (s)   // The number of seconds since the Epoch.
(int32) rand		// A pseudo-random number.
(int32)[2] echo	    // Print every value written to it.

Application

// SPDX-FileCopyrightText: 2020-2023 Jochem Rutgers
//
// SPDX-License-Identifier: CC0-1.0

/*!
 * \file
 * \brief Example to show how functions work.
 */

#include <stored>

#include "ExampleFunction.h"

#include <cstdio>
#include <cstdlib>
#include <ctime>

#ifdef STORED_COMPILER_MSVC
#	pragma warning(disable : 4996)
#endif

// Create a subclass of stored::ExampleFunctionBase to define the side effects of the functions.
class MyExample : public STORE_T(MyExample, stored::ExampleFunctionBase) {
	STORE_CLASS(MyExample, stored::ExampleFunctionBase)
public:
	MyExample()
		: m_echo()
	{}

	// Override the default functions from base. Even though they are not
	// virtual, these are called as expected.  To do this, you had to specify
	// the class as the template parameter of ExampleFunctionBase :)

	// The function gets the parameter set, which indicates if the value is
	// written (true) or should be returned (false).
	void __time_s(bool set, uint64_t& value)
	{
		if(set)
			return; // read-only

		value = (uint64_t)time(nullptr);
	}

	void __rand(bool set, int32_t& value)
	{
		if(!set) {
			uint32_t a = 48271;
			uint32_t m = 2147483647;
			static uint32_t seed = 42;
			value = (int32_t)(seed = (a * seed) % m);
		}
	}

	void __echo_0(bool set, int32_t& value)
	{
		__echo(0, set, value);
	}

	void __echo_1(bool set, int32_t& value)
	{
		__echo(1, set, value);
	}

private:
	void __echo(int i, bool set, int32_t& value)
	{
		assert(i >= 0 && (size_t)i < sizeof(m_echo) / sizeof(m_echo[0]));

		if(set)
			m_echo[i] = value;
		else
			value = m_echo[i];

		printf("%s echo[%d] = %" PRId32 "\n", set ? "set" : "get", i, value);
	}

private:
	int32_t m_echo[2];
};

int main()
{
	MyExample e;

#if 0
	time_t now = (time_t)e.time_s.get();
	printf("time = %s\n", ctime(&now));
#endif

	printf("rand = %" PRId32 "\n", e.rand.get());
	printf("rand = %" PRId32 "\n", e.rand.get());
	printf("rand = %" PRId32 "\n", e.rand.get());

	e.echo_0.set(10);
	e.echo_1.set(11);
	printf("echo[0] returned %" PRId32 "\n", e.echo_0.get());
	printf("echo[1] returned %" PRId32 "\n", e.find("/echo[1]").function<int32_t>().get());

	return 0;
}

Output

rand = 2027382
rand = 1226992363
rand = 549342533
set echo[0] = 10
set echo[1] = 11
get echo[0] = 10
echo[0] returned 10
get echo[1] = 11
echo[1] returned 11

Store reference

template<typename Base_, typename Implementation_>
class ExampleFunctionObjects

All ExampleFunctionBase’s objects.

Subclassed by stored::ExampleFunctionBase< MyExample >

Public Types

typedef Base_ Base

typedef Implementation_ Implementation

Public Members

impl::StoreFunction<Base, Implementation, ExampleFunctionFunctionMap, 3u> echo_0

echo[0]

impl::StoreFunction<Base, Implementation, ExampleFunctionFunctionMap, 4u> echo_1

echo[1]

impl::StoreFunction<Base, Implementation, ExampleFunctionFunctionMap, 2u> rand

rand

impl::StoreFunction<Base, Implementation, ExampleFunctionFunctionMap, 1u> time_s

time (s)

template<typename Implementation_>
class ExampleFunctionBase : public stored::ExampleFunctionObjects<ExampleFunctionBase<Implementation_>, Implementation_>

Base class with default interface of all ExampleFunction implementations.

Although there are no virtual functions in the base class, subclasses can override them. The (lowest) subclass must pass the Implementation_ template paramater to its base, such that all calls from the base class can be directed to the proper overridden implementation.

The base class cannot be instantiated. If a default implementation is required, which does not have side effects to functions, instantiate stored::ExampleFunction. This class contains all data of all variables, so it can be large. So, be aware when instantiating it on the stack. Heap is fine. Static allocations is fine too, as the constructor and destructor are trivial.

To inherit the base class, you can use the following template:

class ExampleFunction : public stored::store<ExampleFunction, ExampleFunctionBase>::type {
    STORE_CLASS(ExampleFunction, ExampleFunctionBase)
public:
    // Your class implementation, such as:
    ExampleFunction() is_default
    // ...
};

Some compilers or tools may get confused by the inheritance using stored::store or stored::store_t. Alternatively, use STORE_T(...) instead, providing the template parameters of stored::store as macro arguments.

See also

stored::ExampleFunction

See also

stored::ExampleFunctionData

Subclassed by stored::ExampleFunctionDefaultFunctions< ExampleFunctionBase< ExampleFunction > >

Public Types

enum [anonymous]

Values:

enumerator ObjectCount

Number of objects in the store.

enumerator VariableCount

Number of variables in the store.

enumerator FunctionCount

Number of functions in the store.

enumerator BufferSize

Buffer size.

typedef Implementation_ Implementation

Type of the actual implementation, which is the (lowest) subclass.

typedef uintptr_t Key

Type of a key.

See also

bufferToKey()

typedef Map<String::type, Variant<Implementation>>::type ObjectMap

Map as generated by map().

typedef ExampleFunctionObjects<ExampleFunctionBase, Implementation_> Objects

typedef ExampleFunctionBase root

We are the root, as used by STORE_CLASS.

typedef ExampleFunctionBase self

Define self for stored::store.

Public Functions

inline ~ExampleFunctionBase()

void __echo_0(bool set, int32_t &value)

Callback for echo[0].

void __echo_1(bool set, int32_t &value)

Callback for echo[1].

void __rand(bool set, int32_t &value)

Callback for rand.

void __time_s(bool set, uint64_t &value)

Callback for time (s)

inline Key bufferToKey(void const *buffer) const noexcept

Converts a variable’s buffer to a key.

A key is unique for all variables of the same store, but identical for the same variables across different instances of the same store class. Therefore, the key can be used to synchronize between instances of the same store. A key does not contain meta data, such as type or length. It is up to the synchronization library to make sure that these properties are handled well.

For synchronization, when hookEntryX() or hookEntryRO() is invoked, one can compute the key of the object that is accessed. The key can be used, for example, in a key-to-Variant map. When data arrives from another party, the key can be used to find the proper Variant in the map.

This way, data exchange is type-safe, as the Variant can check if the data format matches the expected type. However, one cannot process data if the key is not set yet in the map.

inline Type::type bufferToType(void const *buffer) noexcept

Return the type of the variable, given its buffer.

inline Variant<Implementation> echo_a(int a) noexcept

Array-lookup accessor for echo[a].

inline Variant<Implementation> find(char const *name, size_t len = std::numeric_limits<size_t>::max()) noexcept

Finds an object with the given name.

Returns:

the object, or an invalid stored::Variant if not found.

template<typename T>
inline Function<T, Implementation> function(char const *name, size_t len = std::numeric_limits<size_t>::max()) noexcept

Finds a function with the given name.

The function, when it exists, must have the given (fixed) type.

inline Implementation const &implementation() const noexcept

Returns the reference to the implementation.

inline Implementation &implementation() noexcept

Returns the reference to the implementation.

template<typename F>
inline void list(F &&f) noexcept

Calls a callback for every object in the longDirectory().

See also

stored::list()

template<typename F>
inline void list(F f, void *arg, char const *prefix, String::type *nameBuffer) noexcept

Calls a callback for every object in the longDirectory().

See also

stored::list()

template<typename F>
inline void list(F f, void *arg, char const *prefix = nullptr) noexcept

Calls a callback for every object in the longDirectory().

See also

stored::list()

inline uint8_t const *longDirectory() const noexcept

Retuns the long directory.

When not available, the short directory is returned.

inline ObjectMap map(char const *prefix = nullptr)

Create a name to Variant map for the store.

Generating the map may be expensive and the result is not cached.

inline char const *name() const noexcept

Returns the name of store, which can be used as prefix for stored::Debugger.

inline uint8_t const *shortDirectory() const noexcept

Returns the short directory.

template<typename T>
inline Variable<T, Implementation> variable(char const *name, size_t len = std::numeric_limits<size_t>::max()) noexcept

Finds a variable with the given name.

The variable, when it exists, must have the given (fixed) type.

Public Members

impl::StoreFunction<Base, Implementation, ExampleFunctionFunctionMap, 3u> echo_0

echo[0]

impl::StoreFunction<Base, Implementation, ExampleFunctionFunctionMap, 4u> echo_1

echo[1]

impl::StoreFunction<Base, Implementation, ExampleFunctionFunctionMap, 2u> rand

rand

impl::StoreFunction<Base, Implementation, ExampleFunctionFunctionMap, 1u> time_s

time (s)

Public Static Functions

template<typename T>
static inline constexpr FreeFunction<T, Implementation> freeFunction(char const *name, size_t len = std::numeric_limits<size_t>::max()) noexcept

Finds a function with the given name.

The function, when it exists, must have the given (fixed) type. It is returned as a free function; it is not bound yet to a specific store instance. This function is constexpr for C++14.

template<typename T>
static inline constexpr FreeVariable<T, Implementation> freeVariable(char const *name, size_t len = std::numeric_limits<size_t>::max()) noexcept

Finds a variable with the given name.

The variable, when it exists, must have the given (fixed) type. It is returned as a free variable; it is not bound yet to a specific store instance. This function is constexpr for C++14.

static inline constexpr char const *hash() noexcept

Returns a unique hash of the store.

Friends

friend class impl::StoreFunction

friend class impl::StoreVariable

friend class impl::StoreVariantF

friend class impl::StoreVariantV

friend class stored::FreeVariable

friend class stored::Variant< void >

class MyExample : public stored::ExampleFunctionBase<MyExample>

Public Functions

inline MyExample()

inline void __echo_0(bool set, int32_t &value)

inline void __echo_1(bool set, int32_t &value)

inline void __rand(bool set, int32_t &value)

inline void __time_s(bool set, uint64_t &value)