DMD 0.170 release

[Ary Manzana]

Walter Bright wrote:
> Walter Bright wrote:
>> Added foreach_reverse, which addresses a serious shortcoming.
>>
>> http://www.digitalmars.com/d/changelog.html
> 
> 
> Lots of background for the foreach improvements in:
> 
> http://www.digitalmars.com/d/archives/digitalmars/D/17320.html

What about trees? Now I want foreach_inorder, foreach_preorder and 
foreach_postorder. :-)

What about classes having a function that returns the "opApply" needed? 
Something like this:

---
class Tree {
	
	int delegate(int delegate(inout int)) inorder() {
		return delegate int(int delegate(inout uint) dg) {
			// inorder traversal
		};
	}

         int delegate(int delegate(inout int)) preorder() {
		return delegate int(int delegate(inout int) dg) {
			// preorder traversal
		};
	}

         int delegate(int delegate(inout int)) postorder() {
		return delegate int(int delegate(inout int) dg) {
			// postorder traversal
		};
	}

	// This still works, it is the default traversal
         int opApply(int delegate(inout int) dg) {
		// default traversal
	}
	
}

void main() {
	Tree t = giveMeSomeTree();
	
	foreach(int i : t.inorder) {
		// something
         }

	foreach(int i : t.preorder) {
		// something
         }

	foreach(int i : t.postorder) {
		// something
         }

	foreach(int i : t) {
		// something
         }

}
---

Could something like this be done? I think it has the clearest syntax: 
no new keywords needed and very flexible. The compiler should check that 
the right side of the foreach is an array, or a class or struct having 
opApply, or a delegate of the singature I mentioned before.

Ary