April 20, 2012
On Friday, 20 April 2012 at 11:23:49 UTC, Steven Schveighoffer wrote:
> On Fri, 20 Apr 2012 00:06:41 -0400, H. S. Teoh <hsteoh@quickfur.ath.cx> wrote:
>
>
>> The only complaint is that I couldn't write auto[string] dgs and have
>> the compiler auto-infer the delegate type. :-)
>
> Does this not work?
>
> auto dgs = ...
>
> Also, it doesn't look like that needs to be in the inner loop.  Each time you specify an AA literal, it allocates a new one.  So you are allocating another AA literal per line.
>
> -Steve

auto dgs =
[
  "name":  (string value) {d.name = value; },
  "phone": (string value) => cast(void)(d.phone = value),
  "age":   (string value) => cast(void)(d.age   = value.to!int()),
];

This works... is there a better way, to avoid cast?

April 20, 2012
On 04/20/2012 11:50 AM, Arne wrote:
> On Friday, 20 April 2012 at 11:23:49 UTC, Steven Schveighoffer wrote:
>> On Fri, 20 Apr 2012 00:06:41 -0400, H. S. Teoh
>> <hsteoh@quickfur.ath.cx> wrote:
>>
>>
>>> The only complaint is that I couldn't write auto[string] dgs and have
>>> the compiler auto-infer the delegate type. :-)
>>
>> Does this not work?
>>
>> auto dgs = ...
>>
>> Also, it doesn't look like that needs to be in the inner loop. Each
>> time you specify an AA literal, it allocates a new one. So you are
>> allocating another AA literal per line.
>>
>> -Steve
>
> auto dgs =
> [
> "name": (string value) {d.name = value; },
> "phone": (string value) => cast(void)(d.phone = value),
> "age": (string value) => cast(void)(d.age = value.to!int()),
> ];
>
> This works... is there a better way, to avoid cast?
>

The => syntax replaces:

- parentheses around the parameter if there is only one parameter
- curly brackets
- the return keyword
- the semicolon at the end of the return statement

  http://dlang.org/expression.html#Lambda

So => is most suitable when there is a single return statement.

Ali
April 20, 2012
"Arne" <arne@linux.nu> wrote in message news:qmehxgyksrdxkabvcyiv@forum.dlang.org...
>
> auto dgs =
> [
>   "name":  (string value) {d.name = value; },
>   "phone": (string value) => cast(void)(d.phone = value),
>   "age":   (string value) => cast(void)(d.age   = value.to!int()),
> ];
>
> This works... is there a better way, to avoid cast?
>

Yes: Don't use the lambda syntax when it's not a lambda ;)


April 21, 2012
On Friday, 20 April 2012 at 19:00:29 UTC, Nick Sabalausky wrote:
> "Arne" <arne@linux.nu> wrote in message
> news:qmehxgyksrdxkabvcyiv@forum.dlang.org...
>>
>> auto dgs =
>> [
>>   "name":  (string value) {d.name = value; },
>>   "phone": (string value) => cast(void)(d.phone = value),
>>   "age":   (string value) => cast(void)(d.age   = value.to!int()),
>> ];
>>
>> This works... is there a better way, to avoid cast?
>>
>
> Yes: Don't use the lambda syntax when it's not a lambda ;)

But... but... that sounds entirely too reasonable! ;)
April 21, 2012
On 2012-04-20 20:50, Arne wrote:

> auto dgs =
> [
> "name": (string value) {d.name = value; },
> "phone": (string value) => cast(void)(d.phone = value),
> "age": (string value) => cast(void)(d.age = value.to!int()),
> ];
>
> This works... is there a better way, to avoid cast?

You could try explicitly declare the type of "dgs" and see if that helps.

-- 
/Jacob Carlborg
April 21, 2012
Please bear with my ignorance I'm new to D, but why is that any
better compared to a simple

switch(key){
default: throw Exception("Invalid attribute '%s'".format(key));
case "name": d.name = value;
               break;
...
...
}



On Friday, 20 April 2012 at 04:05:43 UTC, H. S. Teoh wrote:
> 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+)");
> 			if (!m) continue;
>
> 			auto key = m.captures[1];
> 			auto value = m.captures[2];
>
> 			alias void delegate(string key, string value) attrDg;
> 			attrDg[string] dgs = [
> 				"name": delegate(string key, string value) {
> 					d.name = value;
> 				},
> 				"phone": delegate(string key, string value) {
> 					d.phone = value;
> 				},
> 				"age": delegate(string key, string value) {
> 					d.age = to!int(value);
> 				},
> 				...	// whole bunch of other stuff to
> 					// parse different attributes
> 			];
> 			attrDg errordg = delegate(string key, string value) {
> 				throw Exception("Invalid attribute '%s'"
> 					.format(key));
> 			};
>
> 			// This is pure awesomeness:
> 			dgs.get(key.idup, errordg)(key.idup, value.idup);
> 		}
> 		// ... do something with Data
> 	}
>
> Basically, I use std.regex to extract keywords from the input, then use
> an AA to map keywords to code that implement said keyword.  That AA of
> delegates is just pure awesomeness. AA.get's default value parameter
> lets you process keywords and handle errors with a single AA lookup.  I
> mean, this is even better than Perl for this kind of text-processing
> code!
>
> The only complaint is that I couldn't write auto[string] dgs and have
> the compiler auto-infer the delegate type. :-) Additionally, I wasn't
> sure if I could omit the "delegate(string,string)" after each keyword;
> if that's actually allowed, then this would make D totally pwn Perl!!
>
> (I left out some stuff that makes this code even more of a joy to write:
> using nested try/catch blocks, I can throw exceptions from deep-down
> parsing code and have the loop that loops over input lines automatically
> prefix error messages with the filename/line number where the error
> occurred. This way, even errors thrown by to!int() will be formatted
> nicely. With Perl, this gets extremely messy due to its pathological use
> of $. for line numbers which can get overwritten in unexpected places if
> you're processing more than one file at a time.)
>
> Did I mention I'm totally in love with D?? Seriously. It can handle
> system-level code and "high-level" text-processing code with total
> impunity. What's there not to like?!
>
>
> T


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