Read conditional function parameters during compile time using __traits

[timvol via Digitalmars-d-learn]

Hi! I've a simple array of bytes I received using sockets. What I 
want to do is to calculate the target length of the message. So, 
I defined a calcLength() function for each function code (it's 
the first byte in my array). My problem is that I defined the 
calcLength() function using conditions so that each calcLength 
should be called depending on the respective function code, see 
below:

module example;

private
{
     size_t calcLength(ubyte ubFuncCode)() if ( ubFuncCode == 1 )
     {
         return 10; // More complex calculated value
     }

     size_t calcLength(ubyte ubFuncCode)() if ( ubFuncCode == 2 )
     {
         return 20; // More complex calculated value
     }

     size_t calcLength(ubyte ubFuncCode)() if ( ubFuncCode == 3 )
     {
         return 30; // More complex calculated value
     }
}

size_t doCalcLength(ubyte ubFuncCode)
{
     return calcLength!(ubFuncCode)();
}

int main()
{
     doCalcLength(1);
     return 0;
}

But... how can I execute these functions? I mean, calling 
doCalcLength(1) function says "Variable ubFuncCode cannot be read 
at compile time". So my idea is to create an array during compile 
time using traits (e.g. __traits(allMembers)) and to check this 
later during runtime. For illustration purposes something like 
this:

--> During compile time:

void function()[ubyte] calcLengthArray;

auto tr = __traits(allMembers, example);
foreach ( string s; tr )
{
     calcLengthArray[__trait(get<ubFuncCode>, s)] = s;
}

--> During runtime:

size_t doCalcLength(ubyte ubFuncCode)
{
     auto length = 0;

     if ( ubFuncCode in calcLengthArray )
     {
         length = calcLengthArray[ubFuncCode]!(ubFuncCode)();
     }

     return length;
}

I hope everyone knows what I want to do :). But... does anyone 
know how I can realize that? I don't want to use a switch/case 
structure because the calcLength() functions can be very complex 
and I've over 40 different function codes. So, I think the best 
approach is to use something similar to the one I described.