A few notes on choosing between Go and D for a quick project

Andrei Alexandrescu via Digitalmars-d digitalmars-d at puremagic.com
Fri Mar 13 10:31:09 PDT 2015

On 3/13/15 8:37 AM, Chris wrote:
> Yep. This is part of the "make people feel good about it" approach.
> Plus, we're not selling shit, it's really a good product. In a way, we
> do it the other way around: bad marketing for a good product.

Yah, indeed. Continuing the experiment, I set out to find Go's 
startsWith. So I googled for ``startswith golang''. First hit is 
http://golang.org/pkg/strings/ but there's no StartsWith on that page. 
The second hit is 
which puts me in the right direction - HasPrefix is the name. So I click 
on that and I get to http://golang.org/pkg/strings/#HasPrefix.

That has no example but the signature is obvious enough. Just to verify, 
I click on the "Example" link on the function "Index" below, and I edit 
these lines:

	fmt.Println(strings.Index("chicken", "ken"))
	fmt.Println(strings.Index("chicken", "dmr"))


	fmt.Println(strings.HasPrefix("chicken", "chi"))
	fmt.Println(strings.HasPrefix("chicken", "dmr"))

Click Run produces "true\nfalse" and... I got it.

* * *

Now here's the interesting part. There's a world of difference between 
D's startsWith and Go's HasPrefix. (Not because there's anything wrong 
about HasPrefix.) It's just that startsWith is very powerful - 
disconcertingly so. It is quite literally the ultimate startsWith:

* Works with any combination of UTF8, UTF16, and UTF32.

* Works with not only strings, but any arrays

* Works with array and element (e.g. "abc".startsWith('a')), not only 
array and array

* Equality is too much? You can pass a predicate

* Efficiently looks for multiple prefixes in a single pass, e.g. 
"abc".startsWith("ab", '#')

* Scratch "array", works with any two ranges with comparable elements 
and for any range and comparable element

For example the expression (assuming s is e.g. a string)


opens a file, progressively reads chunks of 4KB, stitches them together 
at no cost, compares against a prefix until it makes a decision, then 
closes the file and returns the result. A putative Go user wouldn't even 
dream of using HasPrefix directly on a stream coming from a file; the 
whole endeavor would be a function that painstakingly takes all of these 
steps by hand.

We need to take the "disconcerting" out the documentation equation while 
still exposing the power. s1.startsWith(s2) is perfectly apt for two 
strings, and that should be immediately apparent to someone who just 
needs that.


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