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6. Datatypes and Protocols > Protocol Introspection
Now that we’ve seen the soft underbelly of protocols in
Example 6-7, we should mention the
convenience functions for introspecting protocols:
extenders, extends?,
and satisfies?, which collectively
provide a supported API for answering common questions about protocols and
their relationships with types.
extenders-
Returns the classes that have been extended to a given protocol. For example, after going through the examples involving the
Measurableprotocol in the last section, we can see which types participate in that protocol:(extenders Measurable) ;= (user.BorderedButton user.Button)
This is the equivalent of asking, “Which classes implement some Java interface
x?” Note that, because types can be extended to satisfy protocols at any point at runtime, these results are only true for the point in time when a protocol is queried viaextenders.
