April 20, 2012 Re: Random D geekout | ||||
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Posted in reply to Steven Schveighoffer | 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?
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April 20, 2012 Re: Random D geekout | ||||
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Posted in reply to Arne | 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 Re: Random D geekout | ||||
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Posted in reply to Arne | "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 Re: Random D geekout | ||||
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Posted in reply to Nick Sabalausky | 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! ;)
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April 21, 2012 Re: Random D geekout | ||||
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Posted in reply to Arne | 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 Re: Random D geekout | ||||
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Posted in reply to H. S. Teoh | 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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