RAII trouble

[Spacen Jasset via Digitalmars-d-learn]

I have the following code in attempt to create an RAII object 
wrapper, but it seems that it might be impossible. The problem 
here is that FT_Init_FreeType is a static which is set at some 
previous time to a function entry point in the FreeType library.


I could use a scope block, but would rather have a self contained 
thing to do the work. Perhaps some sort of mixin is the other 
solution?


The ideal would be to have a struct that can be placed inside a 
function scope, or perhaps as a module global variable. Why does 
Ft_Init_FreeType have to be read at compile time?



text.d(143,15): Error: static variable FT_Init_FreeType cannot be 
read at compile time

text.d(174,43):called from here: initialise()

struct FreeType
{
@disable this();

static FreeType initialise()
{
return FreeType(0);
}

this(int)
{
int error = FT_Init_FreeType(); /// ERROR
enforce(!error);
}

alias library this;

~this()
{
FT_Done_FreeType(library);
}
FT_Library library;
}

FreeType   freeType = FreeType.initialise();

Re: RAII trouble

[Ali Çehreli via Digitalmars-d-learn]

On 11/20/2015 02:56 PM, Spacen Jasset wrote:

> FT_Init_FreeType is a static which is set at some previous time to a
> function entry point in the FreeType library.

> text.d(143,15): Error: static variable FT_Init_FreeType cannot be read
> at compile time

The compiler seems to think that FT_Init_FreeType is a variable. Is that 
really a function pointer? Can you show how it's defined.


My simple test works:

extern (C) int init_func(double){
return 42;
}

static auto my_func = _func;

struct S {
static S init() {
return S(0);
}

this(int) {
my_func(1.5);
}
}

void main() {
auto s = S.init();
}

Ali

Re: RAII trouble

[anonymous via Digitalmars-d-learn]

On 20.11.2015 23:56, Spacen Jasset wrote:

The ideal would be to have a struct that can be placed inside a function
scope, or perhaps as a module global variable. Why does Ft_Init_FreeType
have to be read at compile time?


text.d(143,15): Error: static variable FT_Init_FreeType cannot be read
at compile time
text.d(174,43):called from here: initialise()

struct FreeType
{
 @disable this();

 static FreeType initialise()
 {
 return FreeType(0);
 }

 this(int)
 {
 int error = FT_Init_FreeType(); /// ERROR
 enforce(!error);
 }

 alias library this;

 ~this()
 {
 FT_Done_FreeType(library);
 }
 FT_Library library;
}

FreeType   freeType = FreeType.initialise();



FT_Init_FreeType must be read at compile time, because freeType is a 
module level variable, and initializers for module variables must be 
static values. The initializer is run through CTFE (Compile Time 
Function Evaluation).


Put the initialization/assignment in a function and it should work. That 
function can be a static constructor or the main function:


FreeType freeType = void; /* 'void' prevents default initialization */
static this() {freeType = FreeType.initialise();} /* should work */
void main() {freeType = FreeType.initialise();} /* too */

Re: RAII trouble

[Spacen Jasset via Digitalmars-d-learn]

On Friday, 20 November 2015 at 23:21:03 UTC, anonymous wrote:

[...]
FT_Init_FreeType must be read at compile time, because freeType 
is a module level variable, and initializers for module 
variables must be static values. The initializer is run through 
CTFE (Compile Time Function Evaluation).
Put the initialization/assignment in a function and it should 
work. That function can be a static constructor or the main 
function:



[...]


Yes, I see. I made a mistake. I need to initialize it elsewhere. 
It was quite confusing.


Thanks.

Re: RAII trouble

[Spacen Jasset via Digitalmars-d-learn]

On Friday, 20 November 2015 at 23:35:50 UTC, Spacen Jasset wrote:

On Friday, 20 November 2015 at 23:21:03 UTC, anonymous wrote:

[...]
FT_Init_FreeType must be read at compile time, because 
freeType is a module level variable, and initializers for 
module variables must be static values. The initializer is run 
through CTFE (Compile Time Function Evaluation).
Put the initialization/assignment in a function and it should 
work. That function can be a static constructor or the main 
function:



[...]


Yes, I see. I made a mistake. I need to initialize it 
elsewhere. It was quite confusing.


Thanks.


I Just noticed this trick you posted, that's interesting. Of 
course I couldn't get it working without the void to discard the 
initialization;


FreeType freeType = void; /* 'void' prevents default 
initialization */
static this() {freeType = FreeType.initialise();} /* should work 
*/