Anyone know why this CTFE isn't working?
import std.stdio;struct State { string s; string getString() { return s; } static State opCall(string s) { State ret; ret.s = s; return ret; }}void main() { auto s = State("adf"); pragma(msg, s.getString());}dmd Output: (line 14 is the pragma statement)struct.d(14): Error: variable s cannot be read at compile timestruct.d(14): Error: cannot evaluate s.getString() at compile times.getString()
Rory McGuire
R&D
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Re: Anyone know why this CTFE isn't working?
On Fri, 16 Jul 2010 11:46:48 +0200, Rory McGuire wrote:
> import std.stdio;
>
> struct State {
> string s; string getString() { return s; } static State opCall(string
> s) {
> State ret;
> ret.s = s;
> return ret;
> }
> }
>
> void main() {
> auto s = State("adf");
> pragma(msg, s.getString());
> }
>
> dmd Output: (line 14 is the pragma statement)
>
> struct.d(14): Error: variable s cannot be read at compile time
> struct.d(14): Error: cannot evaluate s.getString() at compile time
> s.getString()
It's not working because s isn't a compile-time quantity. Try:
enum s = State("adf");
-Lars
Re: Anyone know why this CTFE isn't working?
Sorry about the html
On Fri, 16 Jul 2010 11:46:48 +0200, Rory McGuire
wrote:
import std.stdio;
struct State {
string s; string getString() { return s; }
static State opCall(string s) {
State ret;
ret.s = s;
return ret;
}
}
void main() {
auto s = State("adf");
pragma(msg, s.getString());
}
dmd Output: (line 14 is the pragma statement)
struct.d(14): Error: variable s cannot be read at compile time
struct.d(14): Error: cannot evaluate s.getString() at compile time
s.getString()
Re: Anyone know why this CTFE isn't working?
On Friday 16 July 2010 02:46:48 Rory McGuire wrote:
> import std.stdio;
>
> struct State {
> string s; string getString() { return s; }
> static State opCall(string s) {
> State ret;
> ret.s = s;
> return ret;
> }
> }
>
> void main() {
> auto s = State("adf");
> pragma(msg, s.getString());
> }
Make s an enum and it'll work. As it is, it's a local variable created at
runtime rather than a constant at compile-time. So, use
enum s = State("adf");
- Jonathan M Davis
Re: Anyone know why this CTFE isn't working?
On Fri, 16 Jul 2010 11:58:57 +0200, Lars T. Kyllingstad
wrote:
On Fri, 16 Jul 2010 11:46:48 +0200, Rory McGuire wrote:
import std.stdio;
struct State {
string s; string getString() { return s; } static State opCall(string
s) {
State ret;
ret.s = s;
return ret;
}
}
void main() {
auto s = State("adf");
pragma(msg, s.getString());
}
dmd Output: (line 14 is the pragma statement)
struct.d(14): Error: variable s cannot be read at compile time
struct.d(14): Error: cannot evaluate s.getString() at compile time
s.getString()
It's not working because s isn't a compile-time quantity. Try:
enum s = State("adf");
-Lars
Awesome thanks, worked.
So is the difference that "auto s" is a Struct which can change whereas
"enum s" is a constant?
If it is a constant its just "s" that is constant right?
Thanks Lars
-Rory
Re: Anyone know why this CTFE isn't working?
On Fri, 16 Jul 2010 12:05:02 +0200, Jonathan M Davis
wrote:
On Friday 16 July 2010 02:46:48 Rory McGuire wrote:
import std.stdio;
struct State {
string s; string getString() { return s; }
static State opCall(string s) {
State ret;
ret.s = s;
return ret;
}
}
void main() {
auto s = State("adf");
pragma(msg, s.getString());
}
Make s an enum and it'll work. As it is, it's a local variable created at
runtime rather than a constant at compile-time. So, use
enum s = State("adf");
- Jonathan M Davis
Thanks
worked
Re: Anyone know why this CTFE isn't working?
On Fri, 16 Jul 2010 12:12:38 +0200, Rory McGuire wrote:
> On Fri, 16 Jul 2010 11:58:57 +0200, Lars T. Kyllingstad
> wrote:
>
>> On Fri, 16 Jul 2010 11:46:48 +0200, Rory McGuire wrote:
>>
>>> import std.stdio;
>>>
>>> struct State {
>>> string s; string getString() { return s; } static State
>>> opCall(string s) {
>>> State ret;
>>> ret.s = s;
>>> return ret;
>>> }
>>> }
>>>
>>> void main() {
>>> auto s = State("adf");
>>> pragma(msg, s.getString());
>>> }
>>>
>>> dmd Output: (line 14 is the pragma statement)
>>>
>>> struct.d(14): Error: variable s cannot be read at compile time
>>> struct.d(14): Error: cannot evaluate s.getString() at compile time
>>> s.getString()
>>
>> It's not working because s isn't a compile-time quantity. Try:
>>
>> enum s = State("adf");
>>
>> -Lars
>
> Awesome thanks, worked.
>
> So is the difference that "auto s" is a Struct which can change whereas
> "enum s" is a constant?
> If it is a constant its just "s" that is constant right?
>
> Thanks Lars
Yes. Writing "auto s = State("adf");" is equivalent to writing
State s = State("adf");
and since s can change at runtime, it would be meaningless to say that it
has a value at compile time. However, its *initial value*, the struct
literal State("adf"), is known at compile time -- otherwise it would be
impossible to assign it to an enum.
And actually, an enum is not only a constant, it is a manifest constant.
When you declare "enum x = someFixedValue", the compiler will just
replace all later uses of x with someFixedValue. It's basically the same
as using the literal value in those places.
This has the consequence that you can't take the address of an enum, nor
pass an enum by reference. Doing
enum i = 3;
int* p = &i;
is equivalent to
int* p = &3;
which doesn't make sense.
-Lars
