error[E0308]: mismatched types --> $DIR/issue-47486.rs:2:10 | LL | () < std::mem::size_of::<_>(); | ^^^^^^^^^^^^^^^^^^^^^^^^ expected `()`, found `usize` error[E0282]: type annotations needed --> $DIR/issue-47486.rs:3:11 | LL | [0u8; std::mem::size_of::<_>()]; | ^^^^^^^^^^^^^^^^^^^^^^ cannot infer type of the type parameter `T` declared on the function `size_of` | help: consider specifying the generic argument | LL | [0u8; std::mem::size_of::<_>()]; | ~~~~~ error: aborting due to 2 previous errors Some errors have detailed explanations: E0282, E0308. For more information about an error, try `rustc --explain E0282`.