www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.learn - Filling a Tuple-like struct in variadic member

reply RivenTheMage <riven-mage id.ru> writes:
Is it possible to do such thing without using string mixin?

------------
import std.stdio;
import std.metastrings;

struct Key(T...)
{
	static string declareFields() // compile-time
	{
		string declaration;

	        foreach (index, type; T)
			declaration = declaration ~ Format!("%s field_%s;\n", type.stringof, index);

	        return declaration;
	}

	mixin(declareFields());
	uint numFields;

	static string declareFieldsAssignment() // compile-time
	{
		string declaration;
		immutable(string) exceptionMessage = "Argument type mismatch.";

	        foreach (index, type; T)
		{
			declaration = declaration ~
				Format!("if (_arguments[%s] != typeid(%s))\n", index, type.stringof) ~
	        	        	"        throw new Exception(\"" ~ exceptionMessage ~
"\");\n" ~
					"else\n" ~
					"{\n" ~
				Format!("	field_%s = *(cast(%s*) _argptr);\n", index, type.stringof) ~
				Format!("	_argptr += field_%s.sizeof;\n", index) ~
					"}\n\n";
		}

		return declaration;
	}

	void assignFields(...)
	{
		mixin(declareFieldsAssignment());
		numFields = _arguments.length;
	}
}

void main()
{
	Key!(string) testval;

	testval.assignFields("test string");
	writeln(testval);
}
Nov 08 2011
parent reply Philippe Sigaud <philippe.sigaud gmail.com> writes:
On Tue, Nov 8, 2011 at 12:21, RivenTheMage <riven-mage id.ru> wrote:
 Is it possible to do such thing without using string mixin?

Hi, you can use another tuple: struct Key(T...) { T fields; uint numFields = T.length; void assignFields(U...)(U args) if (U.length == T.length) { foreach(i, field; fields) fields[i] = args[i]; } } void main() { Key!(string, int, int delegate(int)) testval; writeln("Numfields: ", testval.numFields); testval.assignFields("abc", 1, (int i) {return i+1;}); writeln(testval); } You can also test at compile-time if U and T are compatible, before the assignement. Or do you really need assignField to work with runtime values ? Philippe
Nov 08 2011
parent RivenTheMage <riven-mage id.ru> writes:
 Or do you really need assignField to work with runtime values ?

Yes, that's the problem.
Nov 08 2011