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WithCleanup

WithCleanup[expr,cleanup]

evaluates expr, running cleanup before returning the result, even if an abort, throw, etc. was generated during the evaluation of expr.

WithCleanup[init,expr,cleanup]

evaluates init before evaluating expr, blocking aborts, throws, etc. in both init and cleanup.

Details

The following types of operations are blocked in various ways in init and cleanup in WithCleanup:

	aborts	Abort and interactive aborts
	constraints	termination based on TimeConstrained, MemoryConstrained
	control transfers	Throw, Confirm, Goto, Break, Continue, …

If an abort is initiated during the evaluation of init, it is not immediately acted upon, and expr is not evaluated, but cleanup is.
If an abort is initiated during the evaluation of expr, that evaluation is aborted, but cleanup is still executed.
If an abort is initiated during the evaluation of cleanup, the abort is postponed until the evaluation of cleanup is complete.
Constraints generated externally through constructions such as TimeConstrained[... WithCleanup[...]... ] behave in WithCleanup like aborts.
If a control transfer whose destination is outside WithCleanup[...] occurs within init or expr, the evaluation of init or expr is terminated, cleanup is evaluated, and then the transfer occurs.
If a control transfer occurs during the evaluation of cleanup, it is not postponed.

Examples

open allclose all

Basic Examples (2)

Clean up the assignment to x before returning the result:

The cleanup is done even if there is an abort in the main expression being evaluated:

The same happens with other types of exceptions:

Scope (2)

The cleanup is executed even though the evaluation is aborted:

The cleanup is done if an external constraint is reached during the evaluation of the main expression:

Constraints internal to WithCleanup are not treated specially:

Applications (1)

Ensure that work files are properly closed even if a computation is interrupted:

The data was safely written to disk:

Similarly, ensure that temporary files are deleted no matter how a computation ends:

The file was successfully deleted:

Properties & Relations (3)

An abort generated during initialization or cleanup will not prevent them from evaluating completely:

An abort during the evaluation of the main expression will cause its evaluation to end immediately:

An external control transfer in any argument will immediately end that argument's evaluation:

Note that the evaluation of the cleanup will happen if the transfer starts in an earlier argument:

In the last argument, the control transfer takes effect immediately:

The initialization and cleanup are effectively wrapped in AbortProtect:

Possible Issues (1)

Computations in the initialization and cleanup cannot be interactively aborted or time-constrained:

Move all nonessential code into the main expression:

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