Description:
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Calling key() method in a new SplFileObject gives 0. This is the expected result.

If you call now fgets() method and again key() method it gives again 0 as a result. I think this is not the expected behavior.

Subsequent calls to fgets() followed by key() method increases the result by 1 (1, 2, 3...). This is again the expected result.

The behavior is the same with SplFileObject::READ_AHEAD flag.

More information:

http://stackoverflow.com/questions/9876999/first-call-to-fgets-in-splfileobject-doesnt-advance-file-key

Consider following text file, test.txt for the Test Script:
1
2
3

Test script:
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<?php
$file = new SplFileObject('test.txt', 'r');
var_dump($file->key());
$line = $file->fgets();
var_dump($file->key());
$line = $file->fgets();
var_dump($file->key());
$line = $file->fgets();
var_dump($file->key());

Expected result:
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int(0) int(1) int(2) int(3)

Actual result:
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int(0) int(0) int(1) int(2)