Re: [Boost-users] mapping strings to indexes at compile time - MPLmap?

"Paul Baxter" writes:

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"Paul Baxter" writes:

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I have a fixed list of parameter names and with each an associated set of attributes. I wish to access the attributes via the parameter name rather than the equivalent list entry index.

In the past, we've created ENUMs with meaningful names to represent the parameter name->index mapping but I can't help feeling there must be a better way usng the name directly without this extra artificial mapping type.

Is there some reason http://www.boost.org/libs/parameter is not appropriate for you?

The parameter library looks like an incredibly useful library, I'm not sure it is what I'm looking for though, but am happy if you could give me an example. I'm looking for something that does the name->index 'lookup' at compile time.

The parameter library does compile-time lookups. args[third_parameter].get_byte_offset() is a possible syntax with the parameter library. The key to the compile-time lookup is that third_parameter is a different type from, e.g., second_parameter,

(Sorry if this fact wasn't made clearer). My initial reading of parameter is that it is solving a different problem.

Some facts: You can't use a string literal as a template parameter in C++, so there is *no way* to use a string literal as a key in a compile-time lookup. Your example, parameter["third parameter"].get_byte_offset(), goes through a function call (operator[]) to get a class object. That part is necessarily a runtime operation.

Each of my configurable classes defines a fixed list of parameter names and associated attributes known at compile time. Rather than accessing via parameter 'list position' 1, I'd like to access attributes of each parameter (such as parameter type, default value, min/max values) via the parameter's name, mainly from a readability and maintainability point of view.

Sounds like the parameter library to me... provided you give up using strings as indices.

If I ever change the list to add/delete a parameter, the parameter 'access' code would require a recompile but pick up its new index automatically.

Sounds like the parameter library to me...

I can't help feeling this should be easy to do and its frustrating that I can't find a way to achieve this other than the aforementioned enum.

My application is a real-time high-speed one with hundreds (sometimes thousands) of configuration parameters. I need to interrogate these in a very short space of time which doesn't allow run-time assessment of strings for matching them.

http://lists.boost.org/Archives/boost/2005/09/93343.php

Since all are known at compile time I'm sure it must be easy to do this. I'm pretty sure when someone shows me the obvious solution I will be very embarrassed, but until then I can do this with a std::map at runtime, but not at compile time.

I'm pretty sure the parameter library is a good -- if not perfect -- match for your problem. Since I've pointed at it twice now, if you're not embarrassed yet, I'll stop pushing ;-) -- Dave Abrahams Boost Consulting www.boost-consulting.com