Restrict implicit opening of existentials based on the generic function's requirements #42085
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This reverts commit 5b0d1fd.
…on's requirements Rather than looking solely at the existential argument of a generic function to determine whether it self-conforms, compare the existential argument against each of the protocols to which the corresponding generic parameter conforms. This better models when the existential value itself will successfully meet the requirements of the generic function, and therefore not require opening. This provides far better source compatibility by not changing semantics of existing, well-formed calls, and eliminates the need to special-case CoW-related operations in the standard library.
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Rather than looking solely at the existential argument of a generic
function to determine whether it self-conforms, compare the
existential argument against each of the protocols to which the
corresponding generic parameter conforms. This better models when the
existential value itself will successfully meet the requirements of
the generic function, and therefore not require opening.
This provides far better source compatibility by not changing
semantics of existing, well-formed calls, and eliminates the need to
special-case CoW-related operations in the standard library.