@safe quiz

[Michel Fortin]

On 2009-12-30 23:41:54 -0500, Michel Fortin <michel.fortin at michelf.com> said:

> Here is a pathetic example of something that does not work currently:
> 
> struct R {
> 	@safe int opApply(int delegate(ref int) z) {
> 		int i = 1;
> 		return z(i); // Error: safe function 'opApply' cannot call system 
> delegate 'z'
> 	}
> }
> 
> @system
> void someSystemFunction() {
> 	R r;
> 	foreach (i; r) { writeln(i); }
> }
> 
> Should I have to write the opApply twice so it can work with both 
> system and safe functions? I sure hope not. Even then, this does not 
> compile either:

I should add that I can write this to move the error somewhere else 
which is more illustrative of my point by tagging the argument as a 
@safe delegate:

struct R {
	@safe int opApply(int delegate(ref int) @safe z) {
		int i = 1;
		return z(i);
	}
}

@system
void someSystemFunction() {
	R r;
	foreach (i; r) { writeln(i); } // Error: function untitled.R.opApply 
(int delegate(ref int) z) is not callable using argument types (int 
delegate(ref int))
}

This version of opApply gives no error if the caller is @safe:

@safe
void someSafeFunction() {
	R r;
	foreach (i; r) { writeln(i); }
}

(Except about writeln not being safe, but that's not a language issue.)

-- 
Michel Fortin
michel.fortin at michelf.com
http://michelf.com/