Slow code, slow

[bauss]

On Friday, 23 February 2018 at 20:35:44 UTC, Rubn wrote:
> 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.

I disagree.

It actually matters a lot for big projects with lots of 
templates, especially nested templates. Gets a whole lot worse 
when it's templates within mixin templates with templates.

It's not just a "0.3" second difference, but can be half a minute 
or even more.