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POUse-cases for reflection
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copied!<p>Recently I was talking to a co-worker about C++ and lamented that there was no way to take a string with the name of a class field and extract the field with that name; in other words, it lacks reflection. He gave me a baffled look and asked when anyone would ever need to do such a thing.</p> <p>Off the top of my head I didn't have a good answer for him, other than "hey, I need to do it right now". So I sat down and came up with a list of some of the things I've actually done with reflection in various languages. Unfortunately, most of my examples come from my web programming in Python, and I was hoping that the people here would have more examples. Here's the list I came up with:</p> <ol> <li><p>Given a config file with lines like<br> x = "Hello World!"<br> y = 5.0<br> dynamically set the fields of some <code>config</code> object equal to the values in that file. (This was what I wished I could do in C++, but actually couldn't do.)</p></li> <li><p>When sorting a list of objects, sort based on an arbitrary attribute given that attribute's name from a config file or web request.</p></li> <li><p>When writing software that uses a network protocol, reflection lets you call methods based on string values from that protocol. For example, I wrote an IRC bot that would translate<br> <code>!some_command arg1 arg2</code><br> into a method call <code>actions.some_command(arg1, arg2)</code> and print whatever that function returned back to the IRC channel.</p></li> <li><p>When using Python's __getattr__ function (which is sort of like method_missing in Ruby/Smalltalk) I was working with a class with a whole lot of statistics, such as late_total. For every statistic, I wanted to be able to add _percent to get that statistic as a percentage of the total things I was counting (for example, stats.late_total_percent). Reflection made this very easy.</p></li> </ol> <p>So can anyone here give any examples from their own programming experiences of times when reflection has been helpful? The next time a co-worker asks me why I'd "ever want to do something like that" I'd like to be more prepared.</p>

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