Variant associative arrays

[evilrat]

On Thursday, 9 May 2013 at 00:10:48 UTC, Byron Heads wrote:
> I have a variant associative array.  In the example below I am 
> wondering
> if there is a way to create the array without having to 
> indicate the
> variant type on all of the values. Would like to be able to 
> write code
> like #2, or something cleaner/better for #1.  This is intended 
> for a
> library. Other option would be variable parameters, not sure 
> how the
> function signature would look for this.
>
> Any ideas, complaints?
>
> import	std.stdio,
> 	std.variant;
>
> alias Algebraic!(string, long) HDType;
>
> void main()
> {
>
> 	// #1 This works
> 	foo(["first" : HDType("John"),
> 		"last" : HDType("Doe"),
> 		"phone" : HDType(1234546)]);
>
> 	// #2 Wont compile, type mismatch string and long
> 	foo(["first" : "John",
> 		"last" : "Doe",
> 		"phone" : 1234546]);
>
> 	// #3 Other idea
> 	bar("first", "John", "last", "Doe", "phone", 12345678);	
>
> }
>
> void foo(HDType[string] attr)
> {
> 	foreach(string k, ref HDType v; attr)
> 	{
> 		writeln(k, ". ", v.toString());
> 	}
> }

first doesn't compile with DMD 2.062 as int implicitly not 
converted to long.

foo func takes associative array, within this example you can use 
type Variant[string] to make life a bit easier(but i can't 
recommend it for ur real code cause we don't know the usage).

and for third func here is example code, though it doesn't takes 
associative array you can rewrite it to suit ur needs, also 
notice that it's a bit dirty and not very readable cause i'm 
superlazy and quite in a hurry, so you can improve it yourself

---------------

void bar(...)
{
	import core.vararg;

	enum string handler = `.visit! (
		// string type handler
		(string s) => write(s, pos %2 == 0 ? ':' : '\n'),
		// long type handler
		(long l) => write(l, pos %2 == 0 ? ':' : '\n')
		)();`;


	for( int pos = 0; pos < _arguments.length ; pos++ )
	{

		if ( _arguments[pos] == typeid(HDType) )
			mixin(`(va_arg!(HDType)(_argptr))` ~ handler );

		else if ( _arguments[pos] == typeid(string) )
			mixin(`HDType(va_arg!(string)(_argptr))` ~ handler );

		else if ( _arguments[pos] == typeid(long) )
			mixin(`HDType(va_arg!(long)(_argptr))` ~ handler );

		else
			throw new Exception("wrong type");
	}
}