Constructor Parameter vs Member Variable

[Christopher Winter]

If you have a struct member variable named `a` and a constructor 
for that struct that takes a parameter named `a`, it isn't 
obvious what the usage of `a` in the body refers to.

```
import std;

struct F
{
     int a;
     int b;

     this(double a)
     {
         writeln(a);
         a = a;
     }
}

void main()
{
     scope f = F(15);

     writeln(f.a);
}
```

The behavior is extremely unintutive, and arguably broken, in 
that it a) compiles and b) will print 15 on the first line and 0 
on the second line. Additionally, if you rename the constructor 
parameter to be `c`, then it fails to compile (because you can't 
assign a double to an int).

Is there a way to have the compiler warn or error in this 
situation? Or in general does anyone know ways to avoid the 
ambiguity, other than just being careful with names?