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But that's just playing with definitions. Rephrase it as "zero runtime cost abstraction" and you get back to the intended meaning. Incidentally your first ques

But that's just playing with definitions. Rephrase it as "zero runtime cost abstraction" and you get back to the intended meaning. Incidentally your first question is one that's very amenable to testing. When does the Rust compiler spend most of it's time? Is it at the checking stage?

optymizer 5y ago
Oh come on now, do you and the parent really have to be those guys who go "well technically they're not zero cost because the programmer has to wait"? Yes, you're technically correct, but also being unreasonable. It was pretty clear that "zero cost abstractions" refers to the runtime aspect. That is the default meaning, there's nothing to "get back to".
- ChrisSD 5y ago
  Huh? That was exactly my point.
aw1621107 5y ago
> When does the Rust compiler spend most of it's time? Is it at the checking stage? rustc has a self-profiler that can be used to answer this question [0], as well as a mode that times compiler passes [1]. There's no single reason the Rust compiler is slow, as it depends quite heavily on the code being compiled. For some codebases, LLVM code takes up most of the time; in other codebases (e.g., extremely generic-heavy codebases), it'll be checking-related passes. [0]: https://github.com/rust-lang/measureme/blob/master/summarize/Readme.md https://github.com/rust-lang/measureme/blob/master/summarize... [1]: https://wiki.alopex.li/WhereRustcSpendsItsTime https://wiki.alopex.li/WhereRustcSpendsItsTime
chongli 5y ago
It isn’t even zero runtime cost abstraction though. Monomorphizing all generic functions increases code size. Increased code size causes more instruction cache pressure which may actually slow things down, depending on the application. I could imagine if you’ve got some very large functions that are called on a wide variety of objects then every call could blow out the Icache and kill the hit rate.
- ben0x539 5y ago
  It's an abstraction over writing out the monomorphized version by hand. Zero-cost doesn't mean using the abstraction gets you the fastest possible implementation of whatever you're doing.
gameswithgo 5y ago
there are some rust programs where the most time is spent in llvm, others hit slow paths in trait bounds analysis, others hit other spots. there is no single hotpath

optymizer 5y ago

Oh come on now, do you and the parent really have to be those guys who go "well technically they're not zero cost because the programmer has to wait"? Yes, you're technically correct, but also being unreasonable. It was pretty clear that "zero cost abstractions" refers to the runtime aspect. That is the default meaning, there's nothing to "get back to".

ChrisSD 5y ago
Huh? That was exactly my point.

aw1621107 5y ago

> When does the Rust compiler spend most of it's time? Is it at the checking stage? rustc has a self-profiler that can be used to answer this question [0], as well as a mode that times compiler passes [1]. There's no single reason the Rust compiler is slow, as it depends quite heavily on the code being compiled. For some codebases, LLVM code takes up most of the time; in other codebases (e.g., extremely generic-heavy codebases), it'll be checking-related passes. [0]: https://github.com/rust-lang/measureme/blob/master/summarize/Readme.md https://github.com/rust-lang/measureme/blob/master/summarize... [1]: https://wiki.alopex.li/WhereRustcSpendsItsTime https://wiki.alopex.li/WhereRustcSpendsItsTime

chongli 5y ago

It isn’t even zero runtime cost abstraction though. Monomorphizing all generic functions increases code size. Increased code size causes more instruction cache pressure which may actually slow things down, depending on the application. I could imagine if you’ve got some very large functions that are called on a wide variety of objects then every call could blow out the Icache and kill the hit rate.

ben0x539 5y ago
It's an abstraction over writing out the monomorphized version by hand. Zero-cost doesn't mean using the abstraction gets you the fastest possible implementation of whatever you're doing.

gameswithgo 5y ago

there are some rust programs where the most time is spent in llvm, others hit slow paths in trait bounds analysis, others hit other spots. there is no single hotpath