[fpc-pascal] Typed constant

[Jonas Maebe]

On 24 Oct 2008, at 21:51, Valdas Jankūnas wrote:

> const
>  MAX_LAIKO_JUOSTA: TLaikoJuosta=(Valanda: 99; Minute: 59);
>
> I want create another constant:
>
> MAX_LAIKO_JUOSTA_MINUTEMIS=MAX_LAIKO_JUOSTA.Valanda*MinsPerHour 
> +MAX_LAIKO_JUOSTA.Minute;
>
> But compiler (I working in Lazarus v0.9.27 r16994 i386-linux-gtk 2  
> (beta); fpc 2.2.2) reported "Error: Illegal expression" and cursor  
> blinks at end of line of new constant. Same error if I try:
>
> MAX_LAIKO_JUOSTA_MINUTEMIS:  
> SmallInt=MAX_LAIKO_JUOSTA.Valanda*MinsPerHour+MAX_LAIKO_JUOSTA.Minute;
>
> I creating constant from a constant. But why I getting that error?

Because a "typed constant" is a bad name chose by Borland for  
"initialised variable". And you cannot use variables (initialised or  
not) in constant expressions.

With {$j-} typed constants become real constants (they cannot be  
changed anymore, unlike in the default {$j+} state), but even then the  
above probably won't work because while parsing the compiler directly  
writes the values of such constants/initialised variables in the  
assembler list rather than constructing some semantic entity which can  
be reused later (so the compiler has no way to retrieve the values of  
such constants when you try to reuse them later on).


Jonas