Algorithm that accepts a _path as an InputRange and a file extension as an InputRange, and returns an InputRange that produces a char string containing the _path given by path, but where the extension has been set to ext.
See Source File
$(SARGONSRC src/sargon/_path/_setext.d)
Copyright (c) 2000-2014, the authors. All rights reserved.
This module is used to manipulate _path strings.