• agorkvmh (21/21) Sep 03 2018 Hi all,
• bauss (8/29) Sep 03 2018 It prints 1, because pragma(msg) is called when the compiler is
• agorkvmh (4/13) Sep 03 2018 Thank you for your quick answer.
• Alex (38/40) Sep 03 2018 Yes. Put a pragma where you static assert for Foo(1).pos equality
• agorkvmh (3/8) Sep 03 2018 Thanks, by the way, the autocomplete suggests me '__ctfeWrite',
• Stefan Koch (3/13) Sep 03 2018 __ctfeWrite was an idea which never got implemented ...

agorkvmh <forengj gmail.com> writes:

Hi all,

Running this:
---
static assert(Foo(1).pos == 2);


struct Foo
{
     this(int i){ advance(); }

     size_t pos =1;

     void advance()
     {
         pragma(msg, pos);
         pos = pos+1;
         pragma(msg, pos);
     }
}

dmd -o- -unittest source/pgs/parser.d
1LU
1LU
---

The static assert passes, but why the second pragma print '1'?

Thanks

bauss <jj_1337 live.dk> writes:

On Monday, 3 September 2018 at 13:39:25 UTC, agorkvmh wrote:
 Hi all,

 Running this:
 ---
 static assert(Foo(1).pos == 2);


 struct Foo
 {
     this(int i){ advance(); }

     size_t pos =1;

     void advance()
     {
         pragma(msg, pos);
         pos = pos+1;
         pragma(msg, pos);
     }
 }

 dmd -o- -unittest source/pgs/parser.d
 1LU
 1LU
 ---

 The static assert passes, but why the second pragma print '1'?

 Thanks

It prints 1, because pragma(msg) is called when the compiler is 
analyzing the code through the semantic process and not when the 
body of the function is executed during CTFE.

And since "pos = pos+1" is a runtime construct (technically) then 
the expression is ignored, unless the function is called during 
CTFE, but by the time the function is called during CTFE then the 
pragma(msg) has already been executed.

agorkvmh <forengj gmail.com> writes:

On Monday, 3 September 2018 at 13:52:24 UTC, bauss wrote:
 On Monday, 3 September 2018 at 13:39:25 UTC, agorkvmh wrote:
 [...]

 It prints 1, because pragma(msg) is called when the compiler is 
 analyzing the code through the semantic process and not when 
 the body of the function is executed during CTFE.

 And since "pos = pos+1" is a runtime construct (technically) 
 then the expression is ignored, unless the function is called 
 during CTFE, but by the time the function is called during CTFE 
 then the pragma(msg) has already been executed.

Thank you for your quick answer.

There is a way to do print the two values at compile time?
What's the best way to debug a CTFE function?

Alex <sascha.orlov gmail.com> writes:

On Monday, 3 September 2018 at 14:00:23 UTC, agorkvmh wrote:
 There is a way to do print the two values at compile time?

Yes. Put a pragma where you static assert for Foo(1).pos equality 
with 2:

--
static assert(Foo(1).pos == 2);
pragma(msg, Foo(1).pos);

struct Foo
{
     this(int i)
	{
		static assert(this.init.pos == 1);
		advance();
	}

     size_t pos = 1;

     void advance()
     {
         pragma(msg, pos);
         pos = pos + 1;
         pragma(msg, pos);
     }
}

void main(){}
--
 What's the best way to debug a CTFE function?

There is none.

 From the Dlang tour:
"CTFE is a mechanism which allows the compiler to execute 
functions at compile time. There is no special set of the D 
language necessary to use this feature - whenever a function just 
depends on compile time known values the D compiler might decide 
to interpret it during compilation."
https://tour.dlang.org/tour/en/gems/compile-time-function-evaluation-ctfe

As no specifics for CTFE writing exist, no specifics for CTFE 
testing exist.

So, the way to choose is the one you did: by putting static 
asserts at the places where you want to assert, that something 
has to have specific values.
I also added another one, before the initialization of the 
struct. I.e., before calling the advance function.

agorkvmh <forengj gmail.com> writes:

On Monday, 3 September 2018 at 15:00:33 UTC, Alex wrote:
 On Monday, 3 September 2018 at 14:00:23 UTC, agorkvmh wrote:
 [...]

 Yes. Put a pragma where you static assert for Foo(1).pos 
 equality with 2:

 [...]

Thanks, by the way, the autocomplete suggests me '__ctfeWrite', 
what is it?

Stefan Koch <uplink.coder googlemail.com> writes:

On Monday, 3 September 2018 at 15:08:57 UTC, agorkvmh wrote:
 On Monday, 3 September 2018 at 15:00:33 UTC, Alex wrote:
 On Monday, 3 September 2018 at 14:00:23 UTC, agorkvmh wrote:
 [...]

 Yes. Put a pragma where you static assert for Foo(1).pos 
 equality with 2:

 [...]

 Thanks, by the way, the autocomplete suggests me '__ctfeWrite', 
 what is it?

__ctfeWrite was an idea which never got implemented ...
it should be a no-op .... iirc.