Fixing computers / Dynamic linking

Who says you can’t fix things any more? (more photos here).

Sitting at work waiting for our C++ application to link reminds me that just because your language can do lots of stuff at compile time doesn’t mean you necessarily want it to do so. Usually with a C++, the linker goes through your code figuring out what address each function will live at, and making each function-call jump to that address. You do almost all the linking work upfront. In contrast, other languages are lazier – they don’t bother doing any work until it’s actually needed, which makes for faster edit/compile cycles because you’re not doing the work upfront. Actually, often these languages forced into being lazy because the information isn’t available at compile time. But contrapositive doesn’t apply: if you have the information you don’t have to be eager. A C++ compiler could delay figuring out which function to call until the first time the function was called. You’d also need to keep all the type information around until runtime, but you’re probably already doing that for debugging purposes anyway. You’d be moving one phase of the compiler from compile-time to run-time.

You might think it would all be much easier to do this stuff by starting with a more dynamic language. but then with “dynamic-C++” you still maintain the benefit of having static typing checking for silly mistakes. Which brings me full circle to a paper which was on LtU recently which discusses this very topic (and which I have yet to read!).

Ah, dynamic languages vs. static languages. Here I am again.

1 reply on “Fixing computers / Dynamic linking”

There is a third option — use an IDE that supports incremental linking. I hear Xcode on Mac OS X does it for C++; I know vendors have provided such environments for various Unixes in the past.

Comments are closed.