DRY (Don't Repeat Yourself)

Macros allow writing DRY code by factoring out the common parts of functions and/or test suites. Here is an example that implements and tests the +=, *= and -= operators on Vec<T>:

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$ rustc --test dry.rs && ./dry running 3 tests test test::mul_assign ... ok test test::add_assign ... ok test test::sub_assign ... ok test result: ok. 3 passed; 0 failed; 0 ignored; 0 measured