如何将字符串转换为 &'static str [英] How to convert a String into a &'static str

问题描述

如何将 String 转换为 &str?更具体地说，我想将其转换为具有 static 生命周期 (&'static str) 的 str.

How do I convert a String into a &str? More specifically, I would like to convert it into a str with the static lifetime (&'static str).

推荐答案

针对 Rust 1.0 更新

您无法从 String 中获取 &'static str 因为 String 可能不会在您的程序的整个生命周期中存活，并且这就是 &'static 生命周期的含义.您只能从中获取由 String 自己的生命周期参数化的切片.

You cannot obtain &'static str from a String because Strings may not live for the entire life of your program, and that's what &'static lifetime means. You can only get a slice parameterized by String own lifetime from it.

要从 String 到切片 &'a str，您可以使用切片语法:

To go from a String to a slice &'a str you can use slicing syntax:

let s: String = "abcdefg".to_owned();
let s_slice: &str = &s[..];  // take a full slice of the string

或者，您可以使用 String 实现 Deref 并执行显式再借用的事实:

Alternatively, you can use the fact that String implements Deref<Target=str> and perform an explicit reborrowing:

let s_slice: &str = &*s;  // s  : String 
                          // *s : str (via Deref<Target=str>)
                          // &*s: &str

还有另一种方法可以实现更简洁的语法，但只有在编译器能够确定所需的目标类型(例如在函数参数或显式类型化的变量绑定中)时才能使用它.它被称为 deref coercion，它允许只使用 & 运算符，编译器将根据上下文:

There is even another way which allows for even more concise syntax but it can only be used if the compiler is able to determine the desired target type (e.g. in function arguments or explicitly typed variable bindings). It is called deref coercion and it allows using just & operator, and the compiler will automatically insert an appropriate amount of *s based on the context:

let s_slice: &str = &s;  // okay

fn take_name(name: &str) { ... }
take_name(&s);           // okay as well

let not_correct = &s;    // this will give &String, not &str,
                         // because the compiler does not know
                         // that you want a &str

请注意，此模式对于 String/&str 不是唯一的 - 您可以将它用于通过 Deref，例如，使用 CString/CStr 和 OsString/OsStr 来自 std::ffi 模块或 PathBuf/来自 std::path 模块的路径.

Note that this pattern is not unique for String/&str - you can use it with every pair of types which are connected through Deref, for example, with CString/CStr and OsString/OsStr from std::ffi module or PathBuf/Path from std::path module.

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