Another round of updates for LibaryEvolution.rst #20158
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Adding new protocol requirements is now a "binary compatible source breaking change" without explicit guarantees about source compatibility. Removing a default from an associated type is not binary compatible because the associated type may itself have been added resiliently, in which case clients that predate the associated type will not be able to instantiate a witness table for the protocol.
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jrose-apple
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Oct 30, 2018
| source-compatible. | ||
| - A new non-type requirement may be added to a protocol, as long as it has an | ||
| unconstrained default implementation in a protocol extension of the | ||
| protocol itself or some other protocol it refines. |
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Hm. I liked it better with the old organization, but I guess this is fine.
| A protocol's associated types are used in computing the "generic signature" | ||
| that uniquely identifies a generic function. Adding an associated type | ||
| could perturb the generic signature and thus change the identity of a | ||
| function, breaking binary compatibility. |
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Glad to be wrong about this.
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Adding new protocol requirements is now a "binary compatible
source breaking change" without explicit guarantees about
source compatibility.
Removing a default from an associated type is not binary
compatible because the associated type may itself have been
added resiliently, in which case clients that predate the
associated type will not be able to instantiate a witness
table for the protocol.