Creates a new `MaybeUninit<T>` in an uninitialized state？？？

[danielesk]

The generic T is associated with the return value of the uninit method in the red area in the figure below, but not in the internal implementation (MaybeUninit { uninit: () }), how is it associated with T, and the size of T is indeterminate, why is it designed that way?

[kornel]

This is a union, so it can be either the uninit field or the value field, and it can be changed at any time, as permitted by union. Look at the new method.

[danielesk]

Another question in the red area in the picture below, I didn't find the mem directory or file in the std directory when I was looking through the rust source code, how is it related?
And I can't understand how the is associated here, can you explain it in detail?

[kornel]

The std crate gets many of its modules from the core crate. mem is defined in core::mem, in library/core/src/mem/mod.rs.

The MaybeUninit::<u32> is the turbofish syntax. Here <u32> isn't a module, but a type argument for MaybeUninit<u32>, but in expressions it needs extra :: to disambiguate it from less than operator.

[steffahn]

@kornel

The MaybeUninit::<u32> is the turbofish syntax.

In case you (or other readers) weren’t aware: you can customize the links to this website to match the turbofish at hand .

[danielesk]

When I use use std::mem::MaybeUninit, how does it find the library/core/src/mem/mod.rs, what is the whole process or implementation mechanism, can you elaborate?

[semicoleon]

It's reexported from std here

rust-lang/rust/blob/316bda89e4a444bd6d4f4434cc3428383ecff88e/library/std/src/lib.rs#L483

[danielesk]

I read the content of the file you sent, but I still have a little bit do not understand which piece in this file for export, export process do not understand you can explain in detail?

[semicoleon]

The link should have automatically highlighted the line, but it's this one pub use core::mem;