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GotW #100 Solution: Preconditions, Part 1

by Herb Sutter

From the article:

We've seen how postconditions are directly related to assertions (see GotWs #97 and #99). So are preconditions, but that in one important way makes them fundamentally different. What is that? And why would having language support benefit us even more for writing preconditions more than for the other two?