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(&library); /// 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 */
----