www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.learn - Problem with UFCS

reply "Michael" <pongad gmail.com> writes:
Hello!
   I have been using D for a while, but only recently paid 
attention to UFCS. For some reason, I can't convince my code to 
compile properly:

void main() {
	import std.range, std.stdio;
	
	auto sqrs = sequence!((a,n) => n*n)(0);
	auto fibs = recurrence!((a,n) => a[n-1]+a[n-2])(1, 1);
	foreach (v; zip(sqrs, fibs).take(10)) writeln(v);
}

The compiler complains about "undefined identifier 'take'". If I 
rewrite the last line to "take(zip(sqrts, fibs), 10)", the 
problem compiles just fine. Is this a compiler bug, or am I 
missing something obvious? I'm using dmd 2.060 on Windows 7.

Thanks,
Michael
Oct 16 2012
next sibling parent "Adam D. Ruppe" <destructionator gmail.com> writes:
On Tuesday, 16 October 2012 at 16:12:06 UTC, Michael wrote:
 void main() {
 	import std.range, std.stdio;

The problem is that UFCS only works on functions in the global scope. The import inside a function makes them local, so it doesn't consider them in it. This is apparently by design; Walter said that just a couple weeks ago, though I don't have the link right now and don't remember what he said the reason was. But if you move those imports outside the function the rest of your code will work.
Oct 16 2012
prev sibling next sibling parent "Jonathan M Davis" <jmdavisProg gmx.com> writes:
On Tuesday, October 16, 2012 18:28:14 Adam D. Ruppe wrote:
 On Tuesday, 16 October 2012 at 16:12:06 UTC, Michael wrote:
 void main() {
 
 import std.range, std.stdio;

The problem is that UFCS only works on functions in the global scope. The import inside a function makes them local, so it doesn't consider them in it. This is apparently by design; Walter said that just a couple weeks ago, though I don't have the link right now and don't remember what he said the reason was. But if you move those imports outside the function the rest of your code will work.

That seems like it goes against the whole "turtles all the way down" principle that made it so that local imports were added in the first place. I wonder what the reasoning was. - Jonathan M Davis
Oct 16 2012
prev sibling parent "Michael" <pongad gmail.com> writes:
Thank you guys. I can't believe that haven't thought of that.
I still feel that this is rather odd though. I would expect to be 
able to use UFCS in the scope that imports those libraries. 
Though I can definitely see how that might lead to obscure bugs.

On Tuesday, 16 October 2012 at 17:07:36 UTC, Jonathan M Davis 
wrote:
 On Tuesday, October 16, 2012 18:28:14 Adam D. Ruppe wrote:
 On Tuesday, 16 October 2012 at 16:12:06 UTC, Michael wrote:
 void main() {
 
 import std.range, std.stdio;

The problem is that UFCS only works on functions in the global scope. The import inside a function makes them local, so it doesn't consider them in it. This is apparently by design; Walter said that just a couple weeks ago, though I don't have the link right now and don't remember what he said the reason was. But if you move those imports outside the function the rest of your code will work.

That seems like it goes against the whole "turtles all the way down" principle that made it so that local imports were added in the first place. I wonder what the reasoning was. - Jonathan M Davis

Oct 18 2012