select( ( select(STDOUT), $| = 1 )[0] );

This only works if the inner select is evaluated before the assignment is, and I can't find any specification of evaluation order (remember ++$a, $a++, ++$a?)

That's why I don't dare to use this idiom, although I see it often. I still prefer STDOUT->autoflush(1) (using IO::Handle). It's shorter too :)

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