Strange behavior with opAssign and static if

[Andre]

Hi,

I have a template structure Decimal which is used in a OrderDb 
structure. The opAssign method in Decimal leads to strange
behavior in the function execute();
The function execute stores the values of OrderDb in a variant
array. Decimals value should be stored as strings. There is
a static if for this condition.

There is a compilation error for the line
arr[i] = __traits(getMember, struc, member);

-> function.main.OrderDb.opAssign (OrderDb p) is not callable using 
argument types ()

This compilation error disappears if I remove the opAssign method
in Decimal.

How can the opAssign of Decimal influence the code path for a non
decimal field?

Kind regards
André

---code---

import std.traits: isInstanceOf;
import std.variant;

struct Decimal(int precision, int scale){
        void opAssign(T)(T d)
                if (isInstanceOf!(Decimal, T)){}

        string toString(){return "10.22";};
}

struct OrderDb{
        string orderId;
        Decimal!(10,2) amount;
}

void main(){
        execute(OrderDb());
}

void execute(T)(T struc){
        Variant[] arr = new Variant[](2);

        foreach (i, member;__traits(allMembers, T)){
		static if (isInstanceOf!(Decimal, typeof(__traits(getMember, struc, 
member)))){
                        // Store decimals as string
                        arr[i] = (__traits(getMember, struc, 
member)).toString();
                } else {
                        // Store other values with their types
                        arr[i] = __traits(getMember, struc, member);
                }
        }
}