Large difference in size for a number of enum types

[erickt]

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I'm not sure if this is a big deal or not, but clippy is reporting that a number of variants have large size differences, which can result in lots of wasted space, or excessive memcpys.

warning: large size difference between variants
  --> src/admin/messages.rs:13:5
   |
13 |     Rpy(AdminRpy)
   |     ^^^^^^^^^^^^^
   |
   = note: #[warn(large_enum_variant)] on by default
   = help: for further information visit https://github.com/Manishearth/rust-clippy/wiki#large_enum_variant
help: consider boxing the large fields to reduce the total size of the enum
   |     Rpy(Box<AdminRpy>)

warning: large size difference between variants
  --> src/admin/messages.rs:36:5
   |
36 |     ReplicaState(VrState),
   |     ^^^^^^^^^^^^^^^^^^^^^
   |
   = help: for further information visit https://github.com/Manishearth/rust-clippy/wiki#large_enum_variant
help: consider boxing the large fields to reduce the total size of the enum
   |     ReplicaState(Box<VrState>),

warning: large size difference between variants
  --> src/vr/vr_fsm.rs:82:5
   |
82 |     Recovery(Recovery),
   |     ^^^^^^^^^^^^^^^^^^
   |
   = help: for further information visit https://github.com/Manishearth/rust-clippy/wiki#large_enum_variant
help: consider boxing the large fields to reduce the total size of the enum
   |     Recovery(Box<Recovery>),

warning: large size difference between variants
  --> src/msg.rs:15:5
   |
15 |     AdminRpy(AdminRpy),
   |     ^^^^^^^^^^^^^^^^^^
   |
   = help: for further information visit https://github.com/Manishearth/rust-clippy/wiki#large_enum_variant
help: consider boxing the large fields to reduce the total size of the enum
   |     AdminRpy(Box<AdminRpy>),

Are there any downsides on introducing boxes in these structures? This ended up being a big win for the compiler's AST.

[andrewjstone]

The only downside would be allocation overhead. However, for these particular messages, they are used infrequently enough that boxing should allow a net win overall. In the future, they may be restructured enough to not require boxing, but I see no problem with it right now.