Sealed trait connections::Slot

[ratijas]

qmetaobject-rs/qmetaobject/src/connections.rs

Line 162 in 5d1f561

/// You should not implement this trait. It is already implemented for FnMut which has the

If this trait would be sealed, it would become impossible to implement by outsiders. It will also make the documentation line "You should not implement this trait" redundant, and enforce such restriction on a type level.

Steps to fix:

1. Define private module seal inside connections
2. Define bare pub trait Seal there
3. Re-declare Slot as Slot: seal::Seal
4. Implement seal::Seal for all relevant types inside connections module

Sample implementation of sealed pattern: https://github.com/ratijas/windows-rust-counters/blob/f03c769242f2c6b4d990155245aebf9a8cfc4a8c/signal-flow/src/interval.rs#L32-L40