Make the error size smaller

[notgull]

The Error struct is six words wide. In comparison, most of the types returned via Result are one or two words wide. This means that there is about four words of space wasted in every Result. This could be fixed by making the Error type smaller, perhaps by Boxing its innards.

[kchibisov]

I'm not sure from where you've got the fact that it's usually 2 words, if simple String is already 3 words, so with discriminant it'll be 4....

[mattfbacon]

so with discriminant it'll be 4....

Not necessarily, because String is niched so for example Result<String, ()> is the same size as String. This works as long as E is one word or less, so Box fits perfectly (assuming thin pointer of course).