Need a data structure where I can map a string to a type

[JUANDENT]

Hi,

Need a certain compile time map m like this:

using Type = typename m["Customer"]::type; // Type would be Customer 

How can i do this?

Regards,
Juan Dent

[Peter87]

What forces you to have the type as a string?

[JUANDENT]

I have the type as a string in the program- one for each table in the database

[Peter87]

But if the string is fixed at compile time why can't you just use the type directly?

using Type = Customer;

Or pass it around using a template argument or whatever...


I don't understand why it needs to be a string unless the string can vary at runtime in which case you will need a different solution.

[jonnin]

I don't know a way to do this directly. There are ways to do it indirectly (eg a union/variant or conditionally triggered) but if there is a slick way to do this without a middleman layer, I don't know the way.

[JUANDENT]

the string is not known until runtime! I recall a structure in boost libraries that allowed this...

[Peter87]

Well, in that case you would have to use some other technique to accomplish what you want. Consider using an enum instead of a string. You could use if/switch to select the correct behaviour. If different "types" use different "data" then you could use a union. Other alternatives are to use variants or inheritance.

[jonnin]

one of the things I wish we had was a standard enum to string and string to enum construct. You can craft one easily enough, but the language seems bent on adding more stuff, this would be a candidate in my eyes. The stringify macro and using good enum names only gets you so far if you wanted a space character and lookup table of strings is awkward.

Boost has a lot that c++ does not... can you use it?

[JUANDENT]

precisely I think boost must have the answer...

[doug4]

I remember doing something like this a couple of decades ago using a Factory pattern, but that was to actually create an object based on a key. And the classes of the objects being created all descended from a common base class.

However, I'm not sure if either of those conditions apply to the question at hand. Just something to consider.

[Peter87]

It's not necessary to use an enum. It was just a suggestion.