newbie question: Can D do this?

clk clk at
Thu Dec 22 07:37:17 PST 2011

Thank you very much for your response.  It looks similar to what I've 
done in javascript by wrapping all function arguments into a single 
object literal but the D alternative you propose is a little to 
convoluted for a beginner like me. Perhaps I'll understand it better 
after I'm done reading the D book.
To bad D doesn't support passing arguments by name.  It makes code so 
much easier to read, especially in large projects.  Even Fortran allows it.
(Christian Keppenne)

> On 20/12/2011 14:18, clk wrote:
I remember a discussion about year ago or so.

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


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
foo.stringof directly displeases DMD
     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.


> End of Digitalmars-d-learn Digest, Vol 71, Issue 34
> ***************************************************

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