One-shot closures. #7244
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One-shot closures. #7244
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Great! I've been needing one shot closures for a very long time. After this lands can we start putting one shot closures in some of the standard libraries? For example, it really hurts that |
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@sstewartgallus No, we can't use them in public interfaces, since they are not on by default. |
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@graydon suggested that once closures not be part of the language for 1.0, but that they might be hidden behind a -Z compile flag as an "experimental feature" in case people decide they need them. Regardless of whether ```-Z once-fns``` is set, this PR will parse the ```once``` keyword and will prevent closures labelled with it from being called more than once. It will also permit moving out of captured vars in heap closures, just to let the runtime writers stop using ```Cell``` sooner. Setting ```-Z once-fns``` only toggles whether the move-out-from-capture privilege is also given for stack closures. r? @nikomatsakis
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@graydon suggested that once closures not be part of the language for 1.0, but that they might be hidden behind a -Z compile flag as an "experimental feature" in case people decide they need them.
Regardless of whether
-Z once-fnsis set, this PR will parse theoncekeyword and will prevent closures labelled with it from being called more than once. It will also permit moving out of captured vars in heap closures, just to let the runtime writers stop usingCellsooner. Setting-Z once-fnsonly toggles whether the move-out-from-capture privilege is also given for stack closures.r? @nikomatsakis