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());
	}
}

Byron Heads:

> 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.
> ...
> 	// #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]);

If your purpose is to write such associative literal without repeating the HDType(), then a possibility is to write the data in a single string, and feed it to a compile-time function that splits it and builds the associative array.

Bye,
bearophile

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");
	}
}

On Thu, 09 May 2013 03:29:06 +0200, evilrat wrote:

> 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");
> 	}
> }



I think I had a large const in there when I tested so it worked then. This gives me a few ideas, but I may try a different API.

On Thu, 09 May 2013 02:33:08 +0200, bearophile wrote:

> Byron Heads:
> 
>> 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.
>> ...
>> 	// #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]);
> 
> If your purpose is to write such associative literal without repeating the HDType(), then a possibility is to write the data in a single string, and feed it to a compile-time function that splits it and builds the associative array.
> 
> Bye,
> bearophile

That approch may work.  Will have to experiment with the API more.