I need to use function `eval` sometimes, but compiler throws an
error: `Error: variable `firstOperand` cannot be read at compile
time`.
```d
import std.array;
import std.format;
public class BinaryOperatorExpression
{
private
{
string operator;
Expression firstExpr;
Expression secondExpr;
}
public final this(T)(string operator, T firstExpr, T secondExpr)
{
this.operator = operator;
this.firstExpr = firstExpr;
this.secondExpr = secondExpr;
}
override public double eval()
{
double firstOperand = firstExpr.eval();
double secondOperand = secondExpr.eval();
return mixin(
format("%d %s %d", firstOperand, operator,
secondOperand)
);
}
}
```
Type `T` exactly has `eval` returning `double'.
How can I make `firstOperand` and `secondOperand` static?
