Write a generic method to replace a family of legacy API methods

Question

I'm writing code using a legacy API whose code I cannot change. There is a family of methods for supported datatypes (int, double, bool, string, APIObject) to do an operation in the API. These take a parameter of the same datatype as indicated in the name of the method. Sample usages as given below

GetIntExp(5)
GetStringExp("Hello")
GetDoubleExp(1.2)
GetDateExp(DateTime.Now)
GetAPIObjectExp(myObject)

The return type respectively, IntExp, StringExp, DoubleExp, DateExp and ObjectExp. All return types inherit from a class (which interestingly is a generic type) StaticOperator<T> where T is the datatype.

Is it possible to write a generic method in my codebase which redirects calls to the suitable API method based on the datatype which is passed in?

Answer 1

Seems to me you don't need a generic method at all, just a wrapper method for each supported argument type:

public IntExp GetExpression(int value)
{
    return GetIntExp(value);
}

public StringExp GetExpression(string value)
{
    return GetStringExp(value);
}

and so on (assuming your goal is to use the same name for all the ways of getting an expression).

Answer 2

Something like

private Dictionary<Type, Func<object, object>> _funcMapping = new Dictionary<Type, Func<object, object>> {
    {typeof(Int), (input) => GetIntExp((int)input)},
    {typeof(string), (input) => GetStringExp((string)input)},
    ...
};

public StaticOperator<TType> GetExp<TType>(TType target) {
    Func<object, object> func;
    if (!_funcMapping.TryGetValue(typeof(TType), out func))
        throw new NotImplementedException();
    return (StaticOperator<TType>)func(target);
} 

is totally possible, but certainly have scaling problems and quite unsafe as requires a lot of casting.

Of course you can rewrite it using if .. elseif .. elseif .. elseif .. else, but all in all it's just a checking if we have a suitable method.