Pardon me for trivial question, Am new to D.


Why would a statement as below fail to compile. The plan is to do some computation at compile-time hence considering the static-if statement which fails to compile. The regular  if-statement compiles but is not useful since it is a runtime construct.

The error message I get is :  Error: variable i cannot be read at compile time




foreach( i; 0..size-1){
		static if  ( i == -1 ){
			//Do something
		}

	}

On 20/07/2015 12:17 a.m., Clayton wrote:
> Pardon me for trivial question, Am new to D.
>
>
> Why would a statement as below fail to compile. The plan is to do some
> computation at compile-time hence considering the static-if statement
> which fails to compile. The regular  if-statement compiles but is not
> useful since it is a runtime construct.
>
> The error message I get is :  Error: variable i cannot be read at
> compile time
>
>
>
>
> foreach( i; 0..size-1){
>          static if  ( i == -1 ){
>              //Do something
>          }
>
>      }

static if is for compile time known constants.
if is for runtime variables.

In this case it would be a runtime variable even if it is known at compile time.
Known at compile time != run at compile time. They overlap yes, just not the same thing.

On Sunday, 19 July 2015 at 12:17:04 UTC, Clayton wrote:
> Pardon me for trivial question, Am new to D.

In D, you can run regular runtime code at compile time in a lot of cases. Just write an ordinary function that returns the data you need, then use it in a static variable initialization.

// example function, notice regular if and variables inside
int calculate(int i) { if(i < 0) return -i; else return i; }


static int value = calculate(5); // this is run at compile time



Ordinary functions will be interpreted if asked for their result in a context that only can be run at compile time, like a static variable initialization or inside a static if.