Generic implementation doesn't work with concrete types

Using Swift
6

Here is how method calls work in swift:

  1. We find all applicable overloads at compile time and pick the most specific one, using static type information.

  2. If the chosen overload is a protocol requirement, we generate code to look up and call the witness.

  3. Otherwise we generate a direct call to the implementation of the chosen overload.

  4. When checking a conformance of a type to a protocol we find the best witness for each protocol requirement, once again using static type information, as in (1). This is what gets called in 2.

I think some people imagine it as being more like:

  1. For every method call, the compiler generates code to collect the dynamic types of all arguments, and does a lookup in some table.

  2. All method declarations are added to this table at runtime.

That’s not how it works though, so if you start with that mental model it won’t match reality.

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