[cbkeller]

This is one of the cases where there's sometimes confusion between the semantics of Julia as a language and the practical implementation of Julia -- just like how Julia is dynamically typed as a matter of language semantics, but compiles to a statically-typed intermediate representation as an implementation detail [1].

While it is not part of the language semantics, there certainly is, in the current implementation, a time at which any given method in Julia is (JAOT) compiled (via SSA-form IR, LLVM IR, and finally to native machine code) -- and whether or not types are able to be inferred at this time is sufficiently important that it has its own name: type stability [e.g., 2], with type-stable code being generally a couple orders of magnitude faster than equivalent type-unstable code.

[1] https://stackoverflow.com/questions/28078089/is-julia-dynami...

[2] https://www.juliabloggers.com/writing-type-stable-julia-code...

[freemint]

For those who don't know JAOT stands for Just-Ahead-Off-Time and refers to the fact that Julias current implementation doesn't do many things associated with JITs today but simply calls an AOT compiler under the assumption that any function gets called often enough in this session for compilation to be amortized.

There are some weak mechanisms to prevent useless overspecialization such as @nospecialize and there are attempts to add smarter recompilation strategies by some packages.