Omit discriminant from nullary univariant enums. #4866
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If an enum is isomorphic to unit, there's no need to use any bits to represent it. The only obvious reason this wasn't the case was because the enum could be C-like and have a user-specified discriminant -- but that value is constant, so it doesn't need to be stored. This change means that all newtype-like enums have the same size (and layout) as their underlying type, which might be a useful property to have, at least in terms of making programs' low-level behavior less surprising.
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If an enum is isomorphic to unit, there's no need to use any bits to represent it. The only obvious reason this wasn't the case was because the enum could be C-like and have a user-specified discriminant -- but that value is constant, so it doesn't need to be stored. This change means that all newtype-like enums have the same size (and layout) as their underlying type, which might be a useful property to have, at least in terms of making programs' low-level behavior less surprising.
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If an enum is isomorphic to unit, there's no need to use any bits to
represent it. The only obvious reason this wasn't the case was because
the enum could be C-like and have a user-specified discriminant -- but
that value is constant, so it doesn't need to be stored.
This change means that all newtype-like enums have the same size (and
layout) as their underlying type, which might be a useful property to
have, at least in terms of making programs' low-level behavior less
surprising.