Add compile time mutable variable type

[Chang Long]

  I need a type can be change on compile time,  it can be 
immutable or mutable at run time.

For example :
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abstract class Template_parameter_Base{
         TypeInto ti;
         string file ;
         size_t  line l;
         string name ;

        this(TypeInto ti, string file, size_t line, string name){
             this.ti = ti ;
             this.file = file ;
            this.line = line ;
            this.name = name ;
         }
}

class Template_parameter(T) : Template_parameter_Base {
        T   value ;
        alias T this;
	void assign(ref T t){
		value = t ;
	}
}

class Template {
          static 
compile_time_mutable(string[Template_parameter_Base])  
template_vars ;

	void assign(string name, string __file__ = __FILE__, size_t 
__line__ =__LINE__, T)(T t) {
		static if( name in template_vars ){
			static parameter = template_vars[name] ;
		} else {
			static parameter = template_vars[name] =  new 
Template_parameter(typeid(T),  __file__, __line__ );
		}
		parameter.assign(t);
	}
	
	string render(){
		// use template_vars comiplate a dynamic link lib ,  and load 
it,  and put the template_vars to it, and run it ,
		// if  dynamic link lib  already exists,  or the templte file 
is not changed, just run it .
	}
}

void main(){
	static tpl = new Template;
	auto  is_login  =  false ;
	tpl.assign!"is_login"( is_login) ) ;
	if( is_login ) {
		tpl.assign!"user"( new User() ) ;
	}
}

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Why I need this is because I need to know all parameters at first 
time call Template.render,  but a lot parameter will not be call 
at run time. so I need a type can be changed at compile time.
the new type is just like mutable type at CTFE.