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| </pre><pre class="rust"><code><span class="comment">// FIXME: Link below is required to render in index |
| </span><span class="doccomment">/// Asserts that the traits support dynamic dispatch |
| /// ([object-safety](https://doc.rust-lang.org/book/ch17-02-trait-objects.html#object-safety-is-required-for-trait-objects)). |
| /// |
| /// This is useful for when changes are made to a trait that accidentally |
| /// prevent it from being used as an [object]. Such a case would be adding a |
| /// generic method and forgetting to add `where Self: Sized` after it. If left |
| /// unnoticed, that mistake will affect crate users and break both forward and |
| /// backward compatibility. |
| /// |
| /// # Examples |
| /// |
| /// When exposing a public API, it's important that traits that could previously |
| /// use dynamic dispatch can still do so in future compatible crate versions. |
| /// |
| /// ``` |
| /// # #[macro_use] extern crate static_assertions; fn main() {} |
| /// trait MySafeTrait { |
| /// fn foo(&self) -> u32; |
| /// } |
| /// |
| /// assert_obj_safe!(std::fmt::Write, MySafeTrait); |
| /// ``` |
| /// |
| /// Works with traits that are not in the calling module: |
| /// |
| /// ``` |
| /// # #[macro_use] extern crate static_assertions; fn main() {} |
| /// mod inner { |
| /// pub trait BasicTrait { |
| /// fn bar(&self); |
| /// } |
| /// assert_obj_safe!(BasicTrait); |
| /// } |
| /// |
| /// assert_obj_safe!(inner::BasicTrait); |
| /// ``` |
| /// |
| /// The following example fails to compile because raw pointers cannot be sent |
| /// between threads safely: |
| /// |
| /// ```compile_fail |
| /// # #[macro_use] extern crate static_assertions; fn main() {} |
| /// assert_impl!(*const u8, Send); |
| /// ``` |
| /// |
| /// The following example fails to compile because generics without |
| /// `where Self: Sized` are not allowed in [object-safe][object] trait methods: |
| /// |
| /// ```compile_fail |
| /// # #[macro_use] extern crate static_assertions; fn main() {} |
| /// trait MyUnsafeTrait { |
| /// fn baz<T>(&self) -> T; |
| /// } |
| /// |
| /// assert_obj_safe!(MyUnsafeTrait); |
| /// ``` |
| /// |
| /// When we fix that, the previous code will compile: |
| /// |
| /// ``` |
| /// # #[macro_use] extern crate static_assertions; fn main() {} |
| /// trait MyUnsafeTrait { |
| /// fn baz<T>(&self) -> T where Self: Sized; |
| /// } |
| /// |
| /// assert_obj_safe!(MyUnsafeTrait); |
| /// ``` |
| /// |
| /// [object]: https://doc.rust-lang.org/book/ch17-02-trait-objects.html#object-safety-is-required-for-trait-objects |
| </span><span class="attribute">#[macro_export] |
| </span><span class="macro">macro_rules! </span>assert_obj_safe { |
| ($(<span class="macro-nonterminal">$xs</span>:path),+ $(,)<span class="question-mark">?</span>) => { |
| $(<span class="kw">const _</span>: <span class="prelude-ty">Option</span><<span class="kw-2">&</span><span class="macro-nonterminal">$xs</span>> = <span class="prelude-val">None</span>;)+ |
| }; |
| } |
| </code></pre></div> |
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