This constructor creates a new shared state that becomes satisfied when bothrhsandrhs.get()become satisfied. Ifrhsis satisfied, butrhs.get()returns an invalid future then the newly created future becomes satisfied with astd::future_errorexception, and the exception error code isstd::future_errc::broken_promise.
Parameter
Name
Description
rhs
future< future< T > > &&
future(future< U > &&)
Creates a future from a future whose result type is convertible to this future's result type.
Parameters
Name
Description
rhs
future< U > &&
class U
typename Enable
future(std::shared_ptr< shared_state_type >)
Parameter
Name
Description
state
std::shared_ptr< shared_state_type >
Functions
get()
Waits until the shared state becomes ready, then retrieves the value stored in the shared state.
Exceptions
Type
Description
...
any exceptions stored in the shared state.
std::future_error
with std::no_state if the future does not have a shared state.
Returns
Type
Description
T
then(F &&)
Attach a continuation to the future.
Attach a callablefuncto be invoked when the future is ready. The return type is a future wrapping the return type offunc.
Side effects:valid() == falseif the operation is successful.
Parameters
Name
Description
func
F &&
a Callable to be invoked when the future is ready. The function might be called immediately, e.g., if the future is ready.
typename F
Returns
Type
Description
future< >
future<T>where T isstd::result_of_t<F, R>(basically). If T matchesfuture<U>then it returnsfuture<U>. The returned future will contain the result offunc.
Type Aliases
shared_state_type
Alias Of:typename internal::future_base< T >::shared_state_type
[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Hard to understand","hardToUnderstand","thumb-down"],["Incorrect information or sample code","incorrectInformationOrSampleCode","thumb-down"],["Missing the information/samples I need","missingTheInformationSamplesINeed","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-09-04 UTC."],[[["\u003cp\u003eThe latest version of the \u003ccode\u003efuture\u003c/code\u003e class documentation is 2.37.0-rc, and the page provides links to the documentation for versions dating back to 2.10.1.\u003c/p\u003e\n"],["\u003cp\u003eThe \u003ccode\u003efuture\u003c/code\u003e class implements ISO/IEC TS 19571:2016 \u003ccode\u003efuture<T>\u003c/code\u003e, which includes constructors for creating and unwrapping futures, as well as converting result types.\u003c/p\u003e\n"],["\u003cp\u003eThe \u003ccode\u003eget()\u003c/code\u003e function waits for the shared state to be ready and then retrieves the stored value, invalidating the future for subsequent calls, and it can throw exceptions if it does not have a shared state or has stored exceptions.\u003c/p\u003e\n"],["\u003cp\u003eThe \u003ccode\u003ethen(F &&)\u003c/code\u003e function attaches a continuation function to the future, which is invoked when the future is ready, and it returns a new future containing the result of the provided function.\u003c/p\u003e\n"],["\u003cp\u003eThe type alias \u003ccode\u003eshared_state_type\u003c/code\u003e is aliased to \u003ccode\u003etypename internal::future_base< T >::shared_state_type\u003c/code\u003e.\u003c/p\u003e\n"]]],[],null,["# Class future<T> (2.42.0-rc)\n\nVersion latestkeyboard_arrow_down\n\n- [2.42.0-rc (latest)](/cpp/docs/reference/common/latest/classgoogle_1_1cloud_1_1future)\n- [2.41.0](/cpp/docs/reference/common/2.41.0/classgoogle_1_1cloud_1_1future)\n- [2.40.0](/cpp/docs/reference/common/2.40.0/classgoogle_1_1cloud_1_1future)\n- [2.39.0](/cpp/docs/reference/common/2.39.0/classgoogle_1_1cloud_1_1future)\n- [2.38.0](/cpp/docs/reference/common/2.38.0/classgoogle_1_1cloud_1_1future)\n- [2.37.0](/cpp/docs/reference/common/2.37.0/classgoogle_1_1cloud_1_1future)\n- [2.36.0](/cpp/docs/reference/common/2.36.0/classgoogle_1_1cloud_1_1future)\n- [2.35.0](/cpp/docs/reference/common/2.35.0/classgoogle_1_1cloud_1_1future)\n- [2.34.0](/cpp/docs/reference/common/2.34.0/classgoogle_1_1cloud_1_1future)\n- [2.33.0](/cpp/docs/reference/common/2.33.0/classgoogle_1_1cloud_1_1future)\n- [2.32.0](/cpp/docs/reference/common/2.32.0/classgoogle_1_1cloud_1_1future)\n- [2.31.0](/cpp/docs/reference/common/2.31.0/classgoogle_1_1cloud_1_1future)\n- [2.30.0](/cpp/docs/reference/common/2.30.0/classgoogle_1_1cloud_1_1future)\n- [2.29.0](/cpp/docs/reference/common/2.29.0/classgoogle_1_1cloud_1_1future)\n- [2.28.0](/cpp/docs/reference/common/2.28.0/classgoogle_1_1cloud_1_1future)\n- [2.27.0](/cpp/docs/reference/common/2.27.0/classgoogle_1_1cloud_1_1future)\n- [2.26.0](/cpp/docs/reference/common/2.26.0/classgoogle_1_1cloud_1_1future)\n- [2.25.1](/cpp/docs/reference/common/2.25.1/classgoogle_1_1cloud_1_1future)\n- [2.24.0](/cpp/docs/reference/common/2.24.0/classgoogle_1_1cloud_1_1future)\n- [2.23.0](/cpp/docs/reference/common/2.23.0/classgoogle_1_1cloud_1_1future)\n- [2.22.1](/cpp/docs/reference/common/2.22.1/classgoogle_1_1cloud_1_1future)\n- [2.21.0](/cpp/docs/reference/common/2.21.0/classgoogle_1_1cloud_1_1future)\n- [2.20.0](/cpp/docs/reference/common/2.20.0/classgoogle_1_1cloud_1_1future)\n- [2.19.0](/cpp/docs/reference/common/2.19.0/classgoogle_1_1cloud_1_1future)\n- [2.18.0](/cpp/docs/reference/common/2.18.0/classgoogle_1_1cloud_1_1future)\n- [2.17.0](/cpp/docs/reference/common/2.17.0/classgoogle_1_1cloud_1_1future)\n- [2.16.0](/cpp/docs/reference/common/2.16.0/classgoogle_1_1cloud_1_1future)\n- [2.15.1](/cpp/docs/reference/common/2.15.1/classgoogle_1_1cloud_1_1future)\n- [2.14.0](/cpp/docs/reference/common/2.14.0/classgoogle_1_1cloud_1_1future)\n- [2.13.0](/cpp/docs/reference/common/2.13.0/classgoogle_1_1cloud_1_1future)\n- [2.12.0](/cpp/docs/reference/common/2.12.0/classgoogle_1_1cloud_1_1future)\n- [2.11.0](/cpp/docs/reference/common/2.11.0/classgoogle_1_1cloud_1_1future)\n- [2.10.1](/cpp/docs/reference/common/2.10.1/classgoogle_1_1cloud_1_1future) \nImplement ISO/IEC TS 19571:2016 `future\u003cT\u003e`.\n\nConstructors\n------------\n\n### future()\n\n### future(future\\\u003c future\\\u003c T \\\u003e \\\u003e \\&\\&)\n\nCreates a new future that unwraps `rhs`. \nThis constructor creates a new shared state that becomes satisfied when both `rhs` and `rhs.get()` become satisfied. If `rhs` is satisfied, but `rhs.get()` returns an invalid future then the newly created future becomes satisfied with a `std::future_error` exception, and the exception error code is `std::future_errc::broken_promise`.\n| **Note:** The technical specification requires this to be a `noexcept` constructor I (coryan) believe this is a defect in the technical specification, as this *creates* a new shared state: shared states are dynamically allocated, and the allocator (which might be the default `operator new`) may raise.\n\n### future(future\\\u003c U \\\u003e \\&\\&)\n\nCreates a future from a future whose result type is convertible to this future's result type.\n\n### future(std::shared_ptr\\\u003c shared_state_type \\\u003e)\n\nFunctions\n---------\n\n### get()\n\nWaits until the shared state becomes ready, then retrieves the value stored in the shared state. \n| **Note:** This operation invalidates the future, subsequent calls will fail, the application should capture the returned value because it would.\n\n### then(F \\&\\&)\n\nAttach a continuation to the future. \nAttach a callable *func* to be invoked when the future is ready. The return type is a future wrapping the return type of *func*.\n\nSide effects: `valid() == false` if the operation is successful.\n\nType Aliases\n------------\n\n### shared_state_type\n\n**Alias Of** : `typename internal::future_base\u003c T \u003e::shared_state_type`"]]
