2 Templates Issues (possibly bugs)

[John Kiro]

Hello there

I've been experimenting with templates & template mixins, and I have some questions & notes, here are they one by one:

1- I define a template like this:

template Template1(T, alias Var, alias Func)
{
	T abc = Func();		//OK.
	T xyz = Var;		//#1 Error: non-constant expression i1
	//Question 1: Why do I have this error?
}

The above error is issued in case I instantiate the template like this for ex:

	Template1!(int, i1, Func1).abc = 3;
Or
	Template1!(int, i1, Func1).xyz = 3;


No error is issued in case I instantiate it using template mixin:

	mixin Template1!(int, i1, Func1);


The normal instantiation works only in case the template is defined like this:

template Template2(T, alias TFunc1, alias TFunc2)
{
	T var1 = TFunc1();
	T var2 = TFunc2();
}

I.e. both are aliases to functions, not variables. So is this a bug?

Note: I used 2 aliases in the above templates, but the behavior is general (i.e. even if template has only 1 alias)


2- Let's define 2 functions to be used with the previous template (template2):

	int Func1()
	{
		return 100;
	}

	int Func2()
	{
		return 200;
	}

Now the next instantiation fails:

  Template2!(int,Func1,Func2).var1;	//Error: var has no effect in expression (var1)

The next one succeeds:

  Template2!(int,Func1,Func2).var1=10;

Next one succeeds as well (even if the instance is not defined before it):	

  writefln("var1 = ",Template2!(int,Func1,Func2).var1);	//value is 100 (as returned by Func1() )
  Template2!(int,Func1,Func2).var1+=30;	//value is now 130
  

The question here is why the 1st one fails?

Also I see a confusion in the expression "Template2!(int,Func1,Func2).var1", it's sometimes equivalent to variable declaration (as in the previous writefln), and sometimes it's equivalent to a symbol (as in the "+=30" statement).. I hope this note would be added to the documentation.

Regards
John