• The convention of the function, indicated by theattribute. This is similar to the language-level @convention attribute, though SIL extends the set of supported conventions with additional distinctions not exposed at the language level:
  • ​​@convention(thin)​​ indicates a "thin" function reference, which uses the Swift calling convention with no special "self" or "context" parameters.
  • ​​@convention(thick)​​ indicates a "thick" function reference, which uses the Swift calling convention and carries a reference-counted context object used to represent captures or other state required by the function. This attribute is implied by ​​@callee_owned​​ or ​​@callee_guaranteed​​.
  • ​​@convention(block)​​ indicates an Objective-C compatible block reference. The function value is represented as a reference to the block object, which is an ​​id​​-compatible Objective-C object that embeds its invocation function within the object. The invocation function uses the C calling convention.
  • ​​@convention(c)​​ indicates a C function reference. The function value carries no context and uses the C calling convention.
  • ​​@convention(objc_method)​​ indicates an Objective-C method implementation. The function uses the C calling convention, with the SIL-level ​​self​​ parameter (by SIL convention mapped to the final formal parameter) mapped to the ​​self​​ and ​​_cmd​​ arguments of the implementation.
  • ​​@convention(method)​​ indicates a Swift instance method implementation. The function uses the Swift calling convention, using the special ​​self​​ parameter.
  • ​​@convention(witness_method)​​ indicates a Swift protocol method implementation. The function's polymorphic convention is emitted in such a way as to guarantee that it is polymorphic across all possible implementors of the protocol.

 

https://github.com/apple/swift/blob/master/docs/SIL.rst#properties-of-types

 


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