recursive equal, and firstDifference functions

[John Colvin]

On Tuesday, 19 March 2013 at 08:25:45 UTC, timotheecour wrote:
> we need a std.algorithm.equalRecurse(T1,T2)(T1 a, T2 b) that 
> compares recursively a and b;
>
> its behavior should be:
>
> if opEqual is defined, call it

The problem is, Object defines opEqual as "bool opEquals(Object 
o){return this is o;}", so that ruins a lot of class comparisons.

An example implementation of what I think you're getting at:

http://dpaste.dzfl.pl/a7889060

bool deep_equal(T)(T a, T b) {
	static if(isInputRange!T)
		return rec_equal(a, b);
	else static if(__traits(isScalar, T) /*|| __traits(hasMember, T, 
"opEquals")*/)
		return a == b;
	else {
		foreach(i, a_field; a.tupleof)
			if(!deep_equal(a_field, b.tupleof[i]))
				return false;
		return true;
	}
}

bool rec_equal(size_t max_depth = size_t.max, R0, R1)(R0 r0, R1 
r1)
	if(NumDims!R0 == NumDims!R1)
{
	static if(NumDims!R0 == 0 || max_depth == 0)
		return r0 == r1;
	else {
		mixin("return " ~
			  replicate("equal!", min(max_depth-1, NumDims!(R0)-1)) ~ 
"equal(r0, r1);"
			 );
	}
}

template NumDims (T) {
	static if(is(ElementType!T == void))
		const NumDims = 0;
	else
		const NumDims = 1 + NumDims!(ElementType!T);
}