Parsing text, conditional text

Question

I have a text template with placehoders that I am parsing to replace placeholders with real values.

Text Template:

Name:%name% Age:%age% 

I am using StringBuilder.Replace () to replace placeholders

 sb.Replace("%name%", Person.Name); 

Now I want to make a more advanced algorithm. Some lines of code are conditional. They must be completely removed.

Text template

 Name:%Name% Age:%age% Employer:%employer% 

The line Employer should appear only when using a person (controlled by the logical variable Person.IsEmployed).

UPDATE: I can use open / close tags. How to find text between lines A and B? Can I use Regex? How?

Answer 1

Your existing template scheme is not reliable enough - you should add more special placeholders, for example, for example:

 Name:%Name% Age:%age% [if IsEmployed] Employer:%employer% [/if] 

You can parse the [if *] blocks using a regular expression (not tested):

 Match[] ifblocks = Regex.Match(input, "\\[if ([a-zA-Z0-9]+)\\]([^\\[]*)\\[/if\\]"); foreach(Match m in ifblocks) { string originalBlockText = m.Groups[0]; string propertyToCheck = m.Groups[1]; string templateString = m.Groups[2]; // check the property that corresponds to the keyword, ie "IsEmployed" // if it true, do the normal replacement on the templateString // and then replace the originalBlockText with the "filled" templateString // else, just don't write anything out } 

True, although this implementation is full of holes ... Perhaps you will be better off working with template templates, like another answer.

Answer 2

Perhaps you could include the "Employer:" label in the replacement text instead of the template:

Template:

 Name:%Name% Age:%age% %employer% 

Replacement

 sb.Replace("%employer%", string.IsNullOrEmpty(Person.Employer) ? "" : "Employer: " + Person.Employer) 

Answer 3

Another alternative would be to use a template engine such as Spark or NVelocity .

See a quick example for Spark here.

A complete template engine should give you maximum control over the formatted output. For example, conditional and repeating sections.

Answer 4

One option is to make your entire replacement as you are doing now, and then fix the empty variables with the RegEx replacement at the door exit. Something like that:

 Response.Write(RegEx.Replace(sb.ToString(), "\r\n[^:]+:r\n", "\r\n"));