How to make a function that accepts optional struct but can accept struct literal too

[JN via Digitalmars-d-learn]

Is there some nice way of achieving something like this C99 code 
in D?

```c
#include <stdio.h>
typedef struct {
    int x, y;
} inputs_t;

void foo(inputs_t* optional_inputs)
{
    if (!optional_inputs) {
        printf("0 0\n");
    } else {
        printf("%d %d \n", optional_inputs->x, 
optional_inputs->y);
    }
}

int main(void) {
    foo(NULL); // prints 0 0
    foo(&(inputs_t){.x = 5, .y = 6}); // prints 5 6
}
```

below code won't work. Yes, I know I can just use a local 
variable in this case and pass a pointer, but I'd like to get it 
to work with literal structs too.

```d
import std.stdio;

struct inputs_t {
    int x, y;
};

void foo(inputs_t* optional_inputs)
{
    if (!optional_inputs) {
        writeln("0 0");
    } else {
        writeln(optional_inputs.x, optional_inputs.y);
    }
}

void main() {
    foo(null); // prints 0 0
    foo(&(inputs_t(5, 6))); // error: inputs_t(5,6) is not an 
lvalue and cannot be modified
}
```