From: David Flanagan <david@...>
Date: 2007-12-21T07:14:40+09:00
Subject: Re: named captures assigning to local variables

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Attached is a variation on my patch that makes it return $~ instead of 
an array of values.  In testing this I remembered that $~[0] is the 
entire string on the right-hand side, rather than the first captured 
value, so this return value doesn't actually masquerade as an array of 
the assigned values.  So I'm a little less enthusiastic about this 
return value.

(Shouldn't MatchData be Enumerable, by the way?)

	David

David Flanagan wrote:
> Tanaka Akira wrote:
>> In article 
>> <S2445477AbXLTQsI/20071220164808Z+24367@swip003.ftl.affinity.com>,
>>   David Flanagan <david@davidflanagan.com> writes:
>>
>>> How about making the return value an array of the captured strings, 
>>> or nil if there was no match? 
>>
>> Another idea is $~, which is a MatchData or nil.
> 
> That's simpler to implement than what I had done.  And in the simple 
> case when all capturing groups have names, $~ behaves like an array of 
> the captured values, doesn't it?  I think I like this.
> 
> Another option is to raise an exception if the match fails.  I can 
> almost convince myself that this is the right thing to do for this kind 
> of assignment...  But Ruby is usually more forgiving, so probably not.
> 
> Another option is to return an empty array when the pattern fails to 
> match, indicating that no values were assigned.  This follows the 
> example of:
> 
>    x,y = []
> 
> But then you'd have to test the return value with empty? and would have 
> to surround the assignment with parentheses, so the syntax becomes much 
> less pleasant.
> 
>     David
> 
> 


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Index: parse.y
===================================================================
--- parse.y	(revision 14373)
+++ parse.y	(working copy)
@@ -1781,6 +1781,25 @@
 			$$ = dispatch2(assign, $1, $3);
 		    %*/
 		    }
+                | regexp '=' arg
+                    {
+		    /*%%%*/
+			if (!RTEST($1->nd_lit)) {
+			    /* If the regexp has a syntax error,
+			       just pass it up so the error gets reported.
+			       Otherwise we get a segfault in
+			       reg_named_capture_assign */
+			    $$ = $1;
+			}
+			else {
+			    $$ = reg_named_capture_assign($1->nd_lit,
+							  match_op($3, $1));
+			}
+			/* what's the right thing below? */
+		    /*%
+			$$ = dispatch3(binary, $1, ripper_intern("="), $3);
+		    %*/
+                    }
 		| lhs '=' arg modifier_rescue arg
 		    {
 		    /*%%%*/
@@ -2131,9 +2150,6 @@
 		    {
 		    /*%%%*/
 			$$ = match_op($1, $3);
-                        if (nd_type($1) == NODE_LIT && TYPE($1->nd_lit) == T_REGEXP) {
-                            $$ = reg_named_capture_assign($1->nd_lit, $$);
-                        }
 		    /*%
 			$$ = dispatch3(binary, $1, ripper_intern("=~"), $3);
 		    %*/
@@ -8526,6 +8542,7 @@
             )));
     arg->fail_block = block_append(arg->fail_block,
         newline_node(node_assign(assignable(var,0), NEW_LIT(Qnil))));
+
     return ST_CONTINUE;
 }
 
@@ -8542,23 +8559,15 @@
     onig_foreach_name(RREGEXP(regexp)->ptr, reg_named_capture_assign_iter, (void*)&arg);
 
     if (arg.num == 0)
-        return match;
+	compile_error(PARSER_ARG "regular expression on left of destructuring assignment has no named captures");
 
     return 
-        block_append(
-            newline_node(match),
-            NEW_IF(gettable(rb_intern("$~")),
-                block_append(
-                    newline_node(arg.succ_block),
-                    newline_node(
-                        NEW_CALL(
-                          gettable(rb_intern("$~")),
-                          rb_intern("begin"),
-                          NEW_LIST(NEW_LIT(INT2FIX(0)))))),
-                block_append(
-                    newline_node(arg.fail_block),
-                    newline_node(
-                        NEW_LIT(Qnil)))));
+	block_append(
+	    block_append(newline_node(match),
+			 NEW_IF(gettable(rb_intern("$~")),
+				newline_node(arg.succ_block),
+				newline_node(arg.fail_block))),
+	    newline_node(gettable(rb_intern("$~"))));
 }
 
 static VALUE

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