idea for variant improvement

[bioinfornatics]

Variant is very usefull but a function who take a variant as parameter
do not works whithout a cast. but You can assign a value form any type
in statement Variant v = 2u.
the code below explain well the problem
---------------
import std.string;
import std.stdio;
import std.variant;

void func( Variant param ){
    writeln( "it works" );
}

void func2( T )( T param ){
    Variant a = cast(Variant) param;
    writeln( "it works" );
}

void main( string[] args ){
    Variant a = 2u; // works
    func( a );
    //func( 2u ); // does not works
    func2( 2u );
}
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It will be great if function func work in all case