generalize the `read` sender factory

[ericniebler]

Issue by ericniebler
Tuesday Jul 19, 2022 at 22:24 GMT
Originally opened as NVIDIA/stdexec#538

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read(cpo) is a sender that fetches the value of the query cpo from the receiver's environment and sends it through the value channel. Here are two ideas for making it more general:

• Support reading multiple CPOs at a time; e.g., read(cpo1, cpo2, cpo3) would read three values from the receiver and send them all through the value channel.
• Support a way to specify a default value to use if the receiver's environment doesn't implement the CPO; e.g., read(with(cpo, value)).

See also #539, #540

[ericniebler]

Comment by miscco
Wednesday Jul 20, 2022 at 06:24 GMT

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That feels like a monadic interface. would value and value_or fit here?

[ericniebler]

Comment by ericniebler
Saturday Aug 27, 2022 at 16:03 GMT

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Maybe :

when_all(value(cpo1), value_or(cpo2, default))

?