Template mixin Instantiation

[Jorge Lima via Digitalmars-d-learn]

Hi Adam,

Thanks for your explanation.

On Wednesday, 25 May 2016 at 12:15:17 UTC, Adam D. Ruppe wrote:
> On Wednesday, 25 May 2016 at 07:45:32 UTC, Jorge Lima wrote:
>> I can understand that array1 is not expanded to its value 
>> representation in the first call, but why is then when passed 
>> as an argument to the Constructor of the literal argument in 
>> the second call? Am I missing something obvious?
>
> It is just the difference between an alias argument and an 
> ordinary value use.
>
> When passing a name to an alias argument, it retains its 
> identity - `a` in there is now just another name for `array1`. 
> When you `.stringof` it, it sees `a` is an alias for `array1` 
> and pulls it instead.

That part I can somehow grasp.

>
> I suspect you don't actually mean `.stringof` here... that 
> gives the string representation of the identifier; it is what 
> you see in the source (sort of), not the string of the value. 
> `writeln(array)` would make it print out the value of the array.
>

No, my intention was not to print the value of the array. 
Instead, in order to understand mixin template mechanism, I was 
trying to inspect the code generated at the instantiation. I 
thought .stringof would be the way to get it. But I'm also not 
sure about it.

>
> Anyway, if you pass `a` to an ordinary function, like the 
> struct constructor, it is then interpreted as a value instead 
> of as a name of a variable and works the same way as the 
> literal.

I understand the difference between a normal parameter and a 
alias parameter in a mixin template. But shouldn't any 
replacement occur after the code being generated? Assuming that 
.stringof has anything to do with the code generated.

>
> The difference is just on the outside, you aliased a name in 
> one place and a literal in the other place, so that's why 
> .stringof gave different results.

Then, if I understand correctly, what you are saying is that 
array1 in the second instantiation gets replaced by its value 
before being passed to the template. Correct?

This is odd because array1 in the constructor should be passed by 
reference. If it get expanded to a literal, in the context of a 
mixin template, it no longer refers to the same data.

I wonder if this is a bug in the implementation of mixin 
templates.
Again, this assumes that .stringof reflects what code is being 
generated by the template.
Any idea?