Basic Examples (2) 

Evaluate an expression inside OnceUnlessFailed:

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Any subsequent evaluations of OnceUnlessFailed[expr] simply returns the previous result:

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If a message is generated during evaluation, results are not cached:

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Scope (3) 

Retrieve the ResourceFunction:

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Retrieve the ResourceObject:

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Specify an alternate persistence location:

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The value is remembered even after a kernel restart:

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Generalizations & Extensions (3) 

Even if no message is generated, a result will not be cached if the output results in a failure (as determined by FailureQ):

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Since the first evaluation resulted in a failure, the result is not cached:

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The results are now cached:

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Options (3) 

PersistenceTime (2) 

Specify that the result of OnceUnlessFailed should be remembered only for 5 seconds:

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After the time specified has elapsed, the value is recomputed:

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ExpirationDate (1) 

Specify that a remembered value should expire at the beginning of next year:

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Applications (2) 

Use cached cloud operations even if the local machine has an unreliable internet connection:

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The result is only cached once it completes successfully:

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Properties and Relations (1) 

Values for OnceUnlessFailed can be Unset just like Once:

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Possible Issues (2) 

OnceUnlessFailed shares cache locations with Once:

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Using Unset on one will unset the other as well:

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