phobos: What type to use instead of File when doing I/O on streams?

Hello again, I'm a bit puzzled by the "File" type. Looking at the implementation, it seems that all I/O functions were stuffed into a single class^H^H^H^H^Hstruct. What I expected to find is some kind of "Stream" class (with read(), write(), eof()), which is extended by a "File" class (with seek(), mmap(), etc.). So, assuming my program reads from stdin and is supposed to work on a file as well as on a pipe (which is not seekable) - how can I make the compiler bark when I accidently use stdin.seek()? Am I missing something here, too?

On Sunday, 8 November 2015 at 20:47:08 UTC, J.Frank wrote: > Hello again, > > I'm a bit puzzled by the "File" type. Looking at the implementation, it seems that all I/O functions were stuffed into a single class^H^H^H^H^Hstruct. > What I expected to find is some kind of "Stream" class (with read(), write(), eof()), which is extended by a "File" class (with seek(), mmap(), etc.). > > So, assuming my program reads from stdin and is supposed to work on a file as well as on a pipe (which is not seekable) - how can I make the compiler bark when I accidently use stdin.seek()? > > Am I missing something here, too? Use ubyte/char input ranges. Post what you're trying to do if you want an example.

On Sunday, 8 November 2015 at 21:57:55 UTC, Alex Parrill wrote: > Post what you're trying to do if you want an example. $ cat test.d import std.stdio; //void foo(Stream in_stream, Stream out_stream) // I want something like this void foo(File in_stream, File out_stream) { in_stream.seek(3); // BUG string line; while ((line = in_stream.readln()) !is null) out_stream.write(line); } void main(string[] args) { foo(stdin, stdout); } $ cat test.txt Line 0 Line 1 Line 2 $ gdc -o test test.d $ ./test <test.txt e 0 Line 1 Line 2 $ cat test.txt | ./test std.exception.ErrnoException@../../../src/libphobos/std/stdio.d(595): Could not seek in file `' (Illegal seek) $

On Sunday, 8 November 2015 at 20:47:08 UTC, J.Frank wrote: > So, assuming my program reads from stdin and is supposed to work on a file as well as on a pipe (which is not seekable) - how can I make the compiler bark when I accidently use stdin.seek()? You don't, in general. stdin is sometimes seekable and the compiler doesn't know if it is or not until you try at runtime. You could write a wrapper struct for File though that @disables the seek function. It would have a File member, alias file this;, a constructor that forwards to it (optionally, you could also construct it as a File and assign it), and then a @disabled function with the same signature as the seek call in File. Then, it will no longer compile as long as you use your wrapper.

On Sunday, 8 November 2015 at 23:50:58 UTC, Adam D. Ruppe wrote: > You don't, in general. stdin is sometimes seekable and the compiler doesn't know if it is or not until you try at runtime. Hm. "Maybe the stream is seekable, maybe it is not" is not really an option for a language that is supposed to be type safe. I just found std.stream which looks very good. But it is deprecated?? > You could write a wrapper struct for File though that @disables the seek function. It would have a File member, alias file this;, a constructor that forwards to it (optionally, you could also construct it as a File and assign it), and then a @disabled function with the same signature as the seek call in File. Then, it will no longer compile as long as you use your wrapper. Thank you for your solution, but this sounds more lika a hack.

My question is now: How can I make this work without using deprecated stuff? import std.cstream; void foo(InputStream in_stream, OutputStream out_stream) { // in_stream.seek(3); // compile error - good :) char[] line; while ((line = in_stream.readLine()) !is null) out_stream.writeLine(line); } void main(string[] args) { foo(din, dout); }

On 11/09/2015 01:48 AM, J.Frank wrote: > My question is now: > How can I make this work without using deprecated stuff? > > > import std.cstream; > > void foo(InputStream in_stream, OutputStream out_stream) > { > // in_stream.seek(3); // compile error - good :) > > char[] line; > while ((line = in_stream.readLine()) !is null) > out_stream.writeLine(line); > } > > void main(string[] args) > { > foo(din, dout); > } > You don't need the template constraints but it is good practice: import std.stdio; import std.range; void foo(I, O)(I in_stream, O out_stream) if (isInputRange!I && isOutputRange!(O, ElementType!I)) { // in_stream.seek(3); // compile error - good :) foreach (element; in_stream) { out_stream.put(element); } } void main(string[] args) { // Also consider .byLine, which is faster and risky foo(stdin.byLineCopy, stdout.lockingTextWriter); } Ali

On Monday, 9 November 2015 at 14:48:35 UTC, Ali Çehreli wrote: > import std.stdio; > import std.range; > > void foo(I, O)(I in_stream, O out_stream) > if (isInputRange!I && > isOutputRange!(O, ElementType!I)) { > > // in_stream.seek(3); // compile error - good :) > > foreach (element; in_stream) { > out_stream.put(element); > } > } > > void main(string[] args) > { > // Also consider .byLine, which is faster and risky > foo(stdin.byLineCopy, > stdout.lockingTextWriter); > } > > Ali Uhm... no. That's not a solution to my problem. Ranges are not (I/O-)streams.