# newbie question: Can D do this?

Philippe Sigaud philippe.sigaud at gmail.com
Tue Dec 20 12:36:21 PST 2011

```> On 20/12/2011 14:18, clk wrote:
>> Here's another one. Is there a way to pass arguments to functions by
>> keyword as in the
>> calls to f and g below?

I remember a discussion about year ago or so.

It seems doable to have some kind of function transformer (adaptor?) for this.

from:

int foo(int a = 0, int b = 1, double c = 0.0, bool d = false) { return 1;}

alias namedParams!foo nfoo; // transform it into a called-by-name function.

nfoo(["d": true]); // a = 0, b = 1, c = 0.0, d = true
nfoo(["d" : true], ["b" : 100]); // a=0, b=100, c=0.0, d=true
nfoo(1, 2, ["d" : true]);  // a=1, b=2, c=0.0, d=true

That is, it expects some values, then string/values couples as
associative arrays.

Would that be palatable? Because I think it's doable.

To obtain the arguments names:

int foo(int a, int b, double c = 0.0, bool d = true) { return 1;}

template Name(alias foo) if (isCallable!foo)
{
enum string Name = S!(foo.stringof);
}

template S(string s) // this template is just a trick because
{
enum string S = s;
}

writeln(Name!foo); // "int(int a, int b, double c = 0, bool d = true)"

So this gives us:

- the arguments names
- which ones have default values
- what is that default value

The difficulty here is correctly parsing the ( ,,,) part, without
getting desoriented by argument types that themselves use (,), like
templated types.
I think that would make for an small & interesting community challenge.

Philippe
```