学习引用与借用的时候，有一点搞不明白

[gitscofield]

在学习引用与借用的时候，我有一点搞不明白： fn main() { let mut s = String::from("hello, "); let r1 = &mut s; println!("{}",s); // 为什么这里打印s可以 let r2 = &mut s; println!("{}",s); // 为什么这里打印s报错 println!("{}", r2); // 这里打印r2不报错 }

Compiling playground v0.0.1 (/playground) warning: unused variable: r1 --> src/main.rs:14:9	14	let r1 = &mut s;	^^ help: if this is intentional, prefix it with an underscore: _r1

= note: #[warn(unused_variables)] on by default

error[E0502]: cannot borrow s as immutable because it is also borrowed as mutable --> src/main.rs:17:19	16	let r2 = &mut s;	------ mutable borrow occurs here 17	println!("{}",s);	^ immutable borrow occurs here 18	19	println!("{} ", r2);	-- mutable borrow later used here

= note: this error originates in the macro $crate::format_args_nl which comes from the expansion of the macro println (in Nightly builds, run with -Z macro-backtrace for more info)

For more information about this error, try rustc --explain E0502. warning: playground (bin "playground") generated 1 warning error: could not compile playground (bin "playground") due to previous error; 1 warning emitted 🌟🌟