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basic-types/char-bool-unit #182
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basic-types/char-bool-unit
Learning Rust By Practice, narrowing the gap between beginner and skilled-dev with challenging examples, exercises and projects.
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👍 47 -
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❤️ 8 -
🚀 4
Replies: 71 comments 23 replies
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不知道第五行是否少了一个分号,我猜想这应该不是您想考察的地方
fn main() { let _v: () = (); let v = (2, 3); assert_eq!(v, implicitly_ret_unit()) println!("Success!") }
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❤️ 3
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是的,少了,应该是因为最后一行是后面复制过去的
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return (),所以不需要分号
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只有最后一行不需要分号
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加上分号返回(),不加分号print!返回也是().加不加分号效果都一样
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在 Rust 中,语句(Statements)和表达式(Expressions)有一些关键的区别。
- 表达式(Expressions):表达式是计算出某个值的代码片段。例如,
5 + 6是一个表达式,因为它计算出值11。函数调用(如println!("Hello, world!"))和宏调用也是表达式。块{},如果它们以表达式结尾,也是表达式。 - 语句(Statements):语句是执行某些操作但不返回值的代码片段。例如,
let x = 5;是一个语句,因为它创建了一个变量x,但没有返回值。
在 Rust 中,函数体是由一系列语句构成的。如果你想让函数返回一个值,你需要在函数体的最后放一个表达式,而不是语句。这个表达式的值就会成为函数的返回值。注意,这个表达式后面不能有分号,因为在 Rust 中,分号会把表达式转变为语句,而语句不返回值。
例如,以下函数返回一个 i32 类型的值:
fn add_two(x: i32) -> i32 { x + 2 // 这是一个表达式,它的值会被返回 }
如果你在这个表达式后面加上分号,它就变成了一个语句,函数就不会返回值了:
fn add_two(x: i32) -> i32 { x + 2; // 这是一个语句,它不返回值 }
这段代码会导致编译错误,因为函数声明中指定了返回类型 i32,但函数体中没有返回值。
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👍 10
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完成 6/6
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👍 1
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done ! ! !
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完成!第五题的I will returen...是不是手抖拼错了return😳
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checked!
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请问单元类型不占用内存,那么他存放在哪里呢?
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👍 1
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这里元组是空的所以不占内存, 你试着加几个元素进去再试试看?
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只是声明,还没有分配内存,声明应该是不放在内存中,因为内存中一般是为了快速运行。目前它是放在你这个文件中,这是我的理解。
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小白问一下,第一题size_of_val的结果为啥是4,'a'一个字符不是只有一个字节吗
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👍 1
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重温了知识,字符类型就是4个字节,代表Unicode标量值
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👍 10
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没错,字面量是每个4byte,但是字符串不是,1-4任选
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我需要戴眼镜了🧐,第二题我看半天,还以为char有特殊的输出方式,结果。。。
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我也看了半天答案...
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-> 注意,我们还没开始讲字符串,但是这里提前说一下,和一些语言不同,Rust 的字符只能用 '' 来表示, "" 是留给字符串的
我是回去翻的教程
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这样改也可以:
// 修改一行让代码正常打印 fn main() { let c1 = '中'; print_char(c1); } fn print_char(c : &str) { println!("{}", c); }
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done!
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想问下第一题的地方,是不是这个size_of_val()
是因为传入的是一个指针然后这个指针的大小是4B,所以说返回了这个结果?
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我是傻逼
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😄 9
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哈哈哈 🤣
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一般情况下确实256*256两个字节来表示汉字,但是Rust用的是Unicode编码,默认每个字符都是4字节。
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👍 1
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fn main() {
let c1 = '中'; // "" => '' 麻了
print_char(c1);
}
fn print_char(c : char) {
println!("{}", c);
}
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👍 2
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lm
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第5题 implicitly_ret_unit() 返回空元祖吗? ()
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原文如下哦
例如常见的 println!() 的返回值也是单元类型 ()。
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👍 1 -
🎉 1
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done
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Rust 的字符只能用 '' 来表示, "" 是留给字符串的。
字符类型也是占用 4 个字节、布尔值占用内存的大小为 1 个字节、单元类型完全不占用任何内存。
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Done!
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DONE!
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done
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DONE!
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println!("Done");
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day1
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Done!
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done
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I'm done
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✅
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Success(6/6)
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标记完成
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done
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done
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