Expressing preconditions with invariants of parameter types

Everyone who has read Scott Meyer’s books knows: it is a good idea to make your code easy to use correctly and difficult to use incorrectly. In this light, we may be able to improve on the ifs we routinely use to check our functions’ preconditions.

The basic idea is to remove all the ifs that check for error conditions at the beginning of your function’s body by providing type parameters that already give sufficiently strong guarantees.

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