Declaring run time variables

[anonymous via Digitalmars-d-learn]

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);