How can I create a function to access substructure values?

I'd like to write a function which can access the values of a substructure. For example, if I have structure (USA), containing another (states) then values within that substructure, I know I could access the GDP of the state PA through:

USA.PA.GDP

How can I create a generic function, GetGDP so that I can get the same result by

GetGDP(PA).

Similarly, I could enter any state (i.i MD or CA) and return the GDP of that given state.

This is a simplified example of a more complex system, but this is the fundamental challenge I am facing

Answer 1

[Fangjun Jiang]

Using dynamic field names, you don't even need the function. But if you do, it is quite simple.

structName.(dynamicExpression)

USA.PA.GDP=1
USA.MD.GDP=2;

USA.PA.GDP
getGDP(USA,'PA')

function out=getGDP(StructVar,StateName)
out=StructVar.(StateName).GDP;
end