Slow code, slow

[Rubn]

On Friday, 23 February 2018 at 20:15:12 UTC, H. S. Teoh wrote:
> Now that I got your attention:
>
> 	https://issues.dlang.org/show_bug.cgi?id=18511
>
> tl;dr: A trivial piece of code, written as ostensibly 
> "idiomatic D" with std.algorithm and std.range templates, 
> compiles *an order of magnitude* slower than the equivalent 
> hand-written loop.  The way the compiler compiles templates 
> needs some serious improvement.
>
> (And this is why our current fast-fast-fast slogan annoys me so 
> much. One can argue that it's misleading advertising, given 
> that what's considered "idiomatic D", using features like 
> templates and generic code that's highly-touted as D's strong 
> points, compiles a whole order of magnitude slower than C-style 
> D.  Makes me cringe every time I hear "fast code, fast". Our 
> old slogan is a much more accurate description of the current 
> state of things.)
>
>
> T

It's not that big of a slow down. Using "fast" you don't import 
any modules so they never have to be parsed. That's pretty much 
all of phobos you don't have to parse in that example. That's 
just the initial cost too. In a big project this won't make a 
difference. You create a tiny example that is irrelevant to the 
larger scale, that takes 0.3 seconds longer to compile. It's a 
magnitude slower cause in your fast example it's literately only 
parsing 5 lines of code instead of hundreds of lines like it is 
in your slow example.