Re: Declaring run time variables
On Monday, 4 August 2014 at 22:45:15 UTC, anonymous wrote:
On Monday, 4 August 2014 at 22:18:24 UTC, splatterdash wrote:
Indeed I do. I'm not sure which type I should use for the
common base type, though. MyFileReader is a templated class,
so using it plainly did not work. I also tried
`InputRange!string` to no avail despite `MyFileReader`
implementing the three InputRange requirement (popFront(),
front, and empty).
Any ideas on what I should as the class?
Let MyFileReader implement an interface that has the operations
you need. That interface can be std.range.InputRange!string, or
you can define your own.
Note that a type is an input range when it has the input range
primitives (front, popFront, empty), but it's only a
std.range.InputRange!T when it implements the interface in the
OOP sense: class C : InputRange!E {...}.
Phobos generally doesn't use InputRange, but templatizes
everything. You can go that way, too, and move the foreach loop
to a templated function:
void main()
{
File f = File(input_file)
// detect gzip ...
if (isGzip)
doThings(new MyFileReader!GzipIterator(f));
else
doThings(new MyFileReader!NormalIterator(f));
}
void doThings(I)(I fileIter)
{
foreach(string line; fileIter) {
// do things
}
}
That does it, thanks :)!
Best practices for testing functions that opens files
Hi all, Is there a recommended way to test functions that opens and iterates over files? The unittest block seems more suited for testing functions whose input and output can be defined in the program itself. I'm wondering if there is a better way to test functions that open files with specific formats. Thanks before :).
Declaring run time variables
Hello everyone,
I'm trying to write a command-line application that can detect
whether the input file is gzipped or not. Sounds simple enough,
but I can't seem to do it properly in D (this is my first foray
to the language).
After checking whether the file is gzipped or not, I try to
create a new instance of a class that is basically an InputRange
returning each line of the input file:
```
File f = File(input_file)
// detect gzip ...
if (isGzip)
auto fileIter = new MyFileReader!GzipIterator(f)
else
auto fileIter = new MyFileReader!NormalIterator(f)
foreach(string line; fileIter) {
// do things
}
```
However I always get the compiler error `undefined identifier
lineIter`.
Now, my questions are:
1. What is causing the error? Is this caused by the compiler not
being able to figure out what fileIter is at compile time?
2. I realize the current way of creating file handles may not be
the best way to handle gzipped or non-gzipped file. Is there a
better way to detect and create such file handles based on run
time values?
Thanks in advance :).
Re: Declaring run time variables
On Monday, 4 August 2014 at 22:09:49 UTC, anonymous wrote:
On Monday, 4 August 2014 at 22:00:18 UTC, splatterdash wrote:
```
File f = File(input_file)
// detect gzip ...
if (isGzip)
{
auto fileIter = new MyFileReader!GzipIterator(f)
}
else
{
auto fileIter = new MyFileReader!NormalIterator(f)
}
foreach(string line; fileIter) {
// do things
}
```
(Added braces for clarity.)
However I always get the compiler error `undefined identifier
lineIter`.
You have two independent variables called fileIter. Both are
only
available in their respective scopes. Declare the variable
before
the `if` to get one variable with a wider scope:
SomeCommonBaseTypeOfThoseMyFileReaderVariants fileIter;
if (isGzip)
fileIter = new MyFileReader!GzipIterator(f);
else
fileIter = new MyFileReader!NormalIterator(f);
Indeed I do. I'm not sure which type I should use for the common
base type, though. MyFileReader is a templated class, so using it
plainly did not work. I also tried `InputRange!string` to no
avail despite `MyFileReader` implementing the three InputRange
requirement (popFront(), front, and empty).
Any ideas on what I should as the class?
