巨集。系統一律會檢查這些巨集， 但如果是 debug_assert! 這類僅供偵錯的變體，在發布子版本中會編譯為空白內容。 8.4 模式配對 When working with tuples and other structured values it's common to want to extract the inner values into local variables. This can be done manually right) = tuple; println!("left: {left}, right: {right}"); } 38 This works with any kind of structured value: struct Foo { a: i32, b: bool, } fn print_foo(foo: Foo) { let Foo { a, b } = foo; println the example above, the type is (). A variable in the pattern (key in this example) will create a binding that can be used within the match arm. 56 A match guard causes the arm to match only if the condition