Alien expiry
Factor handbook > C library interface > Passing data between Factor and C > Passing pointers to C functions > Alien addresses

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When an image is loaded, any alien objects which persisted from the previous session are marked as having expired. This is because the C pointers they contain are almost certainly no longer valid.

For this reason, the ALIEN: word should not be used in source files, since loading the source file then saving the image will result in the literal becoming expired. Use <alien> instead, and ensure the word calling <alien> is not declared flushable.
expired? ( c-ptr -- ? )