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digitalmars.D.learn - stdio.lines doesn't have popFront, but works with foreach

reply "Andrew Klaassen" <clawsoon yahoo.com> writes:
The docs for stdio.lines say that it's a struct.  stdio.lines 
works with foreach.

The docs for foreach say:

"Iteration over struct and class objects can be done with ranges. 
For foreach, this means the following properties and methods must 
be defined: .empty ... .front ... .popFront()"

But when I try to access any of those properties or methods for 
stdio.lines, I get compilation errors:

   1 import io = std.stdio;
   2
   3 void main(string[] args) {
   4
   5     auto infile = io.File(args[1], "r");
   6
   7     auto filelines = io.lines(infile);
   8
   9     io.writeln(filelines.front);
  10     io.writeln(filelines.empty);
  11     io.writeln(filelines.popFront());
  12 }

test_filechunking.d(9): Error: no property 'front' for type 
'lines'
test_filechunking.d(10): Error: no property 'empty' for type 
'lines'
test_filechunking.d(11): Error: no property 'popFront' for type 
'lines'

Why is this?

I'm using ldc2 for compilation, FWIW.

Andrew
Dec 11 2014
next sibling parent reply "bearophile" <bearophileHUGS lycos.com> writes:
Andrew Klaassen:


 The docs for stdio.lines say that it's a struct.  stdio.lines 
 works with foreach.


If you want a range use "myfile".File.byLine or 
"myfile".File.byLineCopy.

Bye,
bearophile
Dec 11 2014
parent reply "Andrew Klaassen" <clawsoon yahoo.com> writes:
On Thursday, 11 December 2014 at 20:17:50 UTC, bearophile wrote:

 Andrew Klaassen:


 The docs for stdio.lines say that it's a struct.  stdio.lines 
 works with foreach.


 If you want a range use "myfile".File.byLine or 
 "myfile".File.byLineCopy.

 Bye,
 bearophile


I know that there are other ways that'll work.  I was just 
curious about what appears to be a surprise in the way that 
foreach interacts with stdio.lines.

Andrew
Dec 11 2014
parent Steven Schveighoffer <schveiguy yahoo.com> writes:
On 12/11/14 3:21 PM, Andrew Klaassen wrote:

 On Thursday, 11 December 2014 at 20:17:50 UTC, bearophile wrote:

 Andrew Klaassen:


 The docs for stdio.lines say that it's a struct.  stdio.lines works
 with foreach.


 If you want a range use "myfile".File.byLine or "myfile".File.byLineCopy.

 Bye,
 bearophile


 I know that there are other ways that'll work.  I was just curious about
 what appears to be a surprise in the way that foreach interacts with
 stdio.lines.


Look down a little bit further on that document, you will see the 
section titled "Foreach over Structs and Classes with opApply"

Hm.. I note the incorrect statement "If the range properties don't 
exist, then the foreach is defined by the opApply member function". This 
is not exactly true, the foreach statement defaults to opApply first, 
and will use range functions only if that doesn't exist.

FYI, the reason stdio.lines works that way is because in general, ranges 
can only give you one value, but stdio.lines wants to give you the line 
number too.

-Steve
Dec 11 2014
prev sibling parent reply "Kapps" <opantm2+spam gmail.com> writes:
On Thursday, 11 December 2014 at 20:11:21 UTC, Andrew Klaassen 
wrote:

 The docs for stdio.lines say that it's a struct.  stdio.lines 
 works with foreach.

 The docs for foreach say:

 "Iteration over struct and class objects can be done with 
 ranges. For foreach, this means the following properties and 
 methods must be defined: .empty ... .front ... .popFront()"

 But when I try to access any of those properties or methods for 
 stdio.lines, I get compilation errors:

   1 import io = std.stdio;
   2
   3 void main(string[] args) {
   4
   5     auto infile = io.File(args[1], "r");
   6
   7     auto filelines = io.lines(infile);
   8
   9     io.writeln(filelines.front);
  10     io.writeln(filelines.empty);
  11     io.writeln(filelines.popFront());
  12 }

 test_filechunking.d(9): Error: no property 'front' for type 
 'lines'
 test_filechunking.d(10): Error: no property 'empty' for type 
 'lines'
 test_filechunking.d(11): Error: no property 'popFront' for type 
 'lines'

 Why is this?

 I'm using ldc2 for compilation, FWIW.

 Andrew


Ranges are one way of allowing foreach. The other is through the 
use of opApply, which is what std.stdio.lines does.

http://dlang.org/statement.html#ForeachStatement
Dec 11 2014
parent "Andrew Klaassen" <clawsoon yahoo.com> writes:
On Thursday, 11 December 2014 at 20:37:09 UTC, Kapps wrote:

 Ranges are one way of allowing foreach. The other is through 
 the use of opApply, which is what std.stdio.lines does.

 http://dlang.org/statement.html#ForeachStatement


Ah, so I just needed to keep reading down a few lines in the 
foreach docs.  Thanks!

Andrew
Dec 11 2014