swt::Promise< void > Class Reference

Template specialization for void-returning promises. More...

#include <Promise.h>

Collaboration diagram for swt::Promise< void >:

Public Member Functions
	Promise ()
	Default constructor for void promise.
void	set_value ()
	Mark void promise as completed.
void	set_exception (std::exception_ptr exception)
	Reject void promise with an exception.
template<typename F >
auto	then (std::shared_ptr< SLLooper > &looper_, F func) -> Promise< std::invoke_result_t< F > >
	Chain continuation callback for void promise completion.
template<typename F >
auto	catchError (std::shared_ptr< SLLooper > &looper_, F func) -> Promise< void >
	Chain error handler for void promise rejection.
void	operator() ()
	Function call operator for convenient void promise resolution.

Detailed Description

Template specialization for void-returning promises.

This specialization handles promises that represent completion of operations without returning values. Uses std::monostate internally to represent the "no value" state while maintaining the same API as value-returning promises.

Key differences from general template:

• set_value(): Takes no parameters (represents completion)
• Continuation signature: Functions take no parameters
• Internal state: Uses State<std::monostate> instead of State<tValue>
• API consistency: Same chaining and error handling patterns

// Create and resolve void promise
Promise<void> voidPromise;
voidPromise.set_value();  // Mark as completed
 
// Chain operations from void promise
voidPromise.then(looper, []() {
    std::cout << "Void operation completed!" << std::endl;
    return 42;  // Can return value from void continuation
}).then(looper, [](int x) {
    std::cout << "Got value: " << x << std::endl;
});

Note

Specialization maintains API consistency with value-returning promises

std::monostate used internally to represent completion state

See also

Promise, State<std::monostate>

Definition at line 247 of file Promise.h.

Constructor & Destructor Documentation

Promise()

swt::Promise< void >::Promise

(

)

Default constructor for void promise.

Creates a void promise using State<std::monostate> for internal state management while providing a clean void interface.

Note

Implementation in Promise.tpp

Definition at line 7 of file Promise.cpp.

Member Function Documentation

catchError()

template<typename F >

auto swt::Promise< void >::catchError	(	std::shared_ptr< SLLooper > &	looper_,
		F	func
	)		-> Promise< void >

Chain error handler for void promise rejection.

Template Parameters

F	Function type for error handler callback (auto-deduced)

Parameters

looper_	SLLooper instance for callback execution
func	Error handler function that receives std::exception_ptr

Returns

Promise<void> New void promise for further chaining

Registers an error handler for void promise rejection. If the error handler executes successfully (without throwing), the promise chain continues with success state.

Note

Implementation in Promise.tpp

Error handler signature same as general template

voidPromise.catchError(looper, [](std::exception_ptr ex) {
    std::cerr << "Void operation failed, but continuing..." << std::endl;
    // Not throwing means error is handled
}).then(looper, []() {
    std::cout << "Promise chain continues!" << std::endl;
});

See also

Promise, SLLooper

operator()()

void swt::Promise< void >::operator() ( )

inline

Function call operator for convenient void promise resolution.

Convenience operator that allows using the void promise as a callable object for completion marking. Equivalent to calling set_value().

Promise<void> promise;
promise();  // Same as promise.set_value()

Definition at line 355 of file Promise.h.

References swt::Promise< tValue >::set_value().

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set_exception()

void swt::Promise< void >::set_exception

(

std::exception_ptr

exception

)

Reject void promise with an exception.

Parameters

exception

Exception pointer to reject the promise with

Identical behavior to general template - sets promise to failed state and triggers error handlers.

Note

Implementation in Promise.tpp

Thread-safe operation

Definition at line 13 of file Promise.cpp.

set_value()

void swt::Promise< void >::set_value

(

)

Mark void promise as completed.

Resolves the void promise by marking it as completed and triggering any registered continuation callbacks. No value is provided since this represents operation completion.

Note

Implementation in Promise.tpp

Thread-safe operation

Promise<void> promise;
promise.set_value();  // Mark as completed

Definition at line 9 of file Promise.cpp.

then()

template<typename F >

auto swt::Promise< void >::then	(	std::shared_ptr< SLLooper > &	looper_,
		F	func
	)		-> Promise< std::invoke_result_t< F > >

Chain continuation callback for void promise completion.

Template Parameters

F	Function type for continuation callback (auto-deduced)

Parameters

looper_	SLLooper instance for callback execution
func	Continuation function (takes no parameters)

Returns

Promise<ReturnType> New promise for further chaining

Registers a continuation callback that executes when the void promise completes. The continuation function takes no parameters since void promises don't produce values, but can return any type.

Note

Implementation in Promise.tpp

Continuation signature is F() not F(void)

voidPromise.then(looper, []() { 
    return "Void operation completed!"; 
}).then(looper, [](const std::string& msg) {
    std::cout << msg << std::endl;
});

See also

Promise, SLLooper

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The documentation for this class was generated from the following files:

• include/Promise.h
• src/Promise.cpp