Re: Why typeof(template) is void?

2016-07-20 Thread mogu via Digitalmars-d-learn
On Wednesday, 20 July 2016 at 08:01:01 UTC, Lodovico Giaretta 
wrote:

Note that void is a type, while S is not. So you can do:

assert(is(void)) // is(type) returns true
assert(!is(S))   // is(template) returns false;


Thanks very much. I should have noticed this before. T.T


Re: Why typeof(template) is void?

2016-07-20 Thread Lodovico Giaretta via Digitalmars-d-learn

On Wednesday, 20 July 2016 at 05:54:41 UTC, mogu wrote:

On Wednesday, 20 July 2016 at 01:50:37 UTC, Adam D. Ruppe wrote:

On Wednesday, 20 July 2016 at 01:14:05 UTC, mogu wrote:

Why S's type isn't something like `S: (T) -> S`?


Because S isn't a type... think of a template as being like a 
function that returns a type.


int foo(int) { return 0; }

There, you wouldn't expect typeof(foo) to be int, no, 
typeof(foo) is a function that returns an int.


The template is the same thing - it isn't a type, it is a 
template that returns a type.


So it's a higher kinded type aka type class in Haskell. But D's 
reflection cannot get enough information about template's kind. 
Only a `void` given. It may be inconvenient in distinction 
between an alias of template and void. The only solution AFAIK 
is by string of the type property .stringof.


Note that void is a type, while S is not. So you can do:

assert(is(void)) // is(type) returns true
assert(!is(S))   // is(template) returns false;


Re: Why typeof(template) is void?

2016-07-19 Thread mogu via Digitalmars-d-learn

On Wednesday, 20 July 2016 at 01:50:37 UTC, Adam D. Ruppe wrote:

On Wednesday, 20 July 2016 at 01:14:05 UTC, mogu wrote:

Why S's type isn't something like `S: (T) -> S`?


Because S isn't a type... think of a template as being like a 
function that returns a type.


int foo(int) { return 0; }

There, you wouldn't expect typeof(foo) to be int, no, 
typeof(foo) is a function that returns an int.


The template is the same thing - it isn't a type, it is a 
template that returns a type.


So it's a higher kinded type aka type class in Haskell. But D's 
reflection cannot get enough information about template's kind. 
Only a `void` given. It may be inconvenient in distinction 
between an alias of template and void. The only solution AFAIK is 
by string of the type property .stringof.


Re: Why typeof(template) is void?

2016-07-19 Thread Adam D. Ruppe via Digitalmars-d-learn

On Wednesday, 20 July 2016 at 01:14:05 UTC, mogu wrote:

Why S's type isn't something like `S: (T) -> S`?


Because S isn't a type... think of a template as being like a 
function that returns a type.


int foo(int) { return 0; }

There, you wouldn't expect typeof(foo) to be int, no, typeof(foo) 
is a function that returns an int.


The template is the same thing - it isn't a type, it is a 
template that returns a type.