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0 pointsgumby7y ago0 comments

Thanks, I wasn't very clear but now I see the problem. The C++ invocation syntax (basically the difference between expressions and statements inherited from Algol) makes it impossible to call if you want to update it at runtime.

You could declare `static static_map<>::Value& get()` constexpr. (Actually you wouldn't need to; I think you could simply declare `semi::map<>::get()` to be constexpr) and I believe it would allow calling to look up a value to inlined at compile time.

However using it as an lvalue isn't possible with current c++ syntax. As a long time Lisp programmer this limitation continually trips me up.

Sorry about the backquotes; I know that HN doesn't use MD but it was the simplest way to denote code inline.

0 comments

hogliux7y ago

Hmmm, I'm not sure I understand. You can't really mark `static static_map<>::Value& get()` constexpr because it returns a value which is only known at run-time - again the value is a run-time value, only the lookup (where in memory) is at compile-time. This has nothing to do with inlining.

gumbyOP7y ago

Ahh, I looked in the source and see that runtime_map is simply a std::unordered_map.

I didn't look closely enough and assumed you'd made your own hash lookup so that parts of it could be run at compile time (in fact you could intern compile-time keys statically in the front of an object (in the initialized data section of the object file) adding a single additional probe at runtime) and let the linker patch up the locations in the usual fashion.

This is all a move in the right direction!

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