in reply to Re: Runtime introspection: What good is it?
in thread Runtime introspection: What good is it?

This got rather long. Testimony to the thoughtfulness of your use cases; thank you again.

Here are some of the things I've used run-time reflection of some kind for, in various languages:

(My) conclusions

  1. I have no doubt that all of these use cases could be met using a language (like C) that has no introspection capabilities, if the need was strong enough. It might entail using compiler generated ancillary files, or in effect, constructing a limited reflection capability.

  2. As I think I've shown, three of the five above can not only be met using standard OO mechanisms, I would say that those three would be better met that way.

  3. The other two, (grouped together and shown last), are strong use cases for reflection, where that capability is available.

    Though whether they are common enough to warrent the inclusion of introspection in a language is open to debate. If the reflection is done, as in Java, by (as I understand it), pulling apart the bytecode at run-time, the costs when it is not used are negligable.

    But in languages or frameworks where introspection must be support through the retention of compile-time parsing tables or the construction of code tree decorations, the costs in terms of space and time can be significant enough that they should only be done on demand, through the use of compile-time switches or pragmas, not by default.

  4. In general, I think that just as inheritance was overused and abused in the poineering days OO, and still is by novice users, so introspection is equally easily abused. And 5 or 10 years from now, it will probably have gained as bad a rep. when people step back from its rising popularity on the basis of RoR and resurgent interest in Objective-C.

    Like any technology, used sparingly with understanding of the costs, it will serve some use cases in ways that nothing else can.

    But if it is overused, just because it can, to solve at run-time use cases that are better served by compile-time solutions, I see it suffering a backlash as the mainenance costs become evident.

I hope that if anyone read this far, they will find some of this as useful as I have.

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