Random D geekout

[H. S. Teoh]

On Fri, Apr 20, 2012 at 08:44:06AM +0400, Denis Shelomovskij wrote:
> 20.04.2012 8:06, H. S. Teoh написал:
> >I'm writing some code that does some very simplistic parsing, and I'm
> >just totally geeking out on how awesome D is for writing such code:
> >
> >	import std.conv;
> >	import std.regex;
> >	import std.stdio;
> >
> >	struct Data {
> >		string name;
> >		string phone;
> >		int age;
> >		... // a whole bunch of other stuff
> >	}
> >
> >	void main() {
> >		Data d;
> >		foreach (line; stdin.byLine()) {
> >			auto m = match(line, "(\w+)\s+(\w+)");
> 
> It's better not to create a regex every iteration. Use e.g.
> ---
> auto regEx = regex(`(\w+)\s+(\w+)`);
> ---
> before foreach. Of course, you are not claiming this as a
> high-performance program, but creating a regex every iteration is
> too common mistake to show such code to newbies.

You're right, it was unoptimized code. I ended up using ctRegex for
them:

	enum attrRx = ctRegex!`...`;
	enum blockRx = ctRegex!`...`;

	if (auto m = match(line, attrRx)) {
		...
	} else if (auto m = match(line, blockRx)) {
		...
	}

The fact that D enums can be arbitrary types is just beyond awesome.


[...]
> >			auto key = m.captures[1];
> 
> One `.idup` here will be better. (sorry, just like to nitpick)

Yeah you're right. I'm refactoring the code right now, and it's much
better to write it this way:

	auto key = m.captures[1].idup;
	auto value = m.captures[2].idup;
	dgs.get(key, invalidAttr)(key, value);

Looks more concise, too.

[...]
> A shorter variant:
> ---
> void delegate(string, string)[string] dgs = [
> 	"name" : (key, value) { d.name = value; },
> 	"phone": (key, value) { d.phone = value; },
> 	"age"  : (key, value) { d.age = to!int(value); },
> 	...	// whole bunch of other stuff to
> 		// parse different attributes
> ];
[...]

Good idea, I really need to work on my delegate syntax. I must admit I
still have to look it up each time, 'cos I just can't remember the right
syntax with all its shorthands thereof.


T

-- 
Let's not fight disease by killing the patient. -- Sean 'Shaleh' Perry