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4. AN IMPLEMENTATION 4.6. Generation of Original Syntax
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Listing 4.8: Example Metadata
not know what application is being configured at that moment. Therefore, it cannot determine
what delimiters to print on a given pattern (e.g., INI “[]” or XML block delimiters), or how to
print them (e.g., INI single header or XML header and footer). So, to print a file to its original
syntax, there should be enough information regarding the original syntax, in the generic syntax,
for the Printer.
One way to know what delimiters should be print is to store them in a field in the be-
ginning of the file in generic syntax. As the pattern delimiters are immutable throughout the
configuration file (i.e., comments always start with # in an Apache configuration file), infor-
mation regarding them can be unified in a special Metadata field in the beginning of the file.
This makes it possible for the Printer to query Metadata to know what to print on a certain
pattern.
The format of a pattern is of great importance as well. The same pattern might have differ-
ent formats in two different configuration file languages. For instance, an INI block has only
one block header, whereas an XML block (i.e., element) has a header and a footer. Again, since
the Printer does not know what application it is configuring at the moment, it does not know
whether to print a pattern one way or the other.
To solve this problem, a format string which describes how a pattern looks like is associated
with each pattern, forming an FStr field. In this way, the Printer gets the FStr from a pattern
and prints it accordingly. A format string may be composed of the following:
%a.name The value of the attribute named name in the current element is printed;
%e The value of the current element is printed;
%m.name The value of the element named name in Metadata is printed;
%c The format string is in the next child of the current element;
%s A space is printed;
%n A new line is printed;
Let’s consider the following header in an INI configuration file:
[Engine]
The corresponding Metadata is depicted in Listing 4.8 and the FStr will look like Listing 4.9.
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