210dd611aa
The `?` postfix operator is sugar equivalent to the try! macro, but is more amenable to chaining:
`File::open("foo")?.metadata()?.is_dir()`.
`?` is accepted on any *expression* that can return a `Result`, e.g. `x()?`, `y!()?`, `{z}?`,
`(w)?`, etc. And binds more tightly than unary operators, e.g. `!x?` is parsed as `!(x?)`.
cc #31436
21 lines
831 B
Rust
21 lines
831 B
Rust
// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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macro_rules! id {
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($e:expr) => { $e }
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}
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fn main() {
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id!(x?); //~ error: the `?` operator is not stable (see issue #31436)
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//~^ help: add #![feature(question_mark)] to the crate attributes to enable
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y?; //~ error: the `?` operator is not stable (see issue #31436)
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//~^ help: add #![feature(question_mark)] to the crate attributes to enable
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}
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