Add limited CTFE

[mahkoh]

Implement compile time evaluation of a limited set of compiler-internal functions:

• size_of
• min_align_of
• pref_align_of

Rendered

Old rendered link (not working)

EDIT: Fixed rendered link / Centril

[SiegeLord]

I've always thought that it'd be easiest to make all of these be associated statics of the Sized kind.

[steveklabnik]

All new features are going to end up landing behind a feature gate at first, so this part isn't really relevant.

[mahkoh]

I meant that this should be behind a feature gate until real CTFE has been implemented (if ever). Real CTFE would immediately replace this, but because this is not 100% compatible you would have to continue to maintain this if it's not marked unstable in some way.

[Ericson2314]

I've always thought that it'd be easiest to make all of these be associated statics of the Sized kind.

+1. This seems like an excellent workaround until we get "real CTFE".

[nrc]

We discussed this in the triage meeting today, and while CTFE of some kind is something we are interested in, it is backwards compatible and not high enough priority to block 1.0. Therefore we are postponing discussion on this until post-1.0. Thanks for the RFC!

[fschutt]

The "rendered" link in the first comment is broken. Just wanted to report that.

[Centril]

@fschutt Thanks; Fixed =)