How does <param> know the type when not explicitly set?

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I am currently doing a C++ program which executes launchfiles and monitor their processes if they die and I now I wonder how normally the type of the value of the param is selected.

Actually I thought it is saved as string all the time and then depending on what the user decides to have it, trying to be converted.

But when I look at the functions in param.h ... this does not seem to be the case. So how are they checked if they are bool, float, double, string, when no type is given?

Regards,

Christian