lenSliceTo

fn lenSliceTo(ptr: anytype, comptime end: std.meta.Elem(@TypeOf(ptr))) usize {
    switch (@typeInfo(@TypeOf(ptr))) {
        .pointer => |ptr_info| switch (ptr_info.size) {
            .one => switch (@typeInfo(ptr_info.child)) {
                .array => |array_info| {
                    if (array_info.sentinel()) |s| {
                        if (s == end) {
                            return findSentinel(array_info.child, end, ptr);
                        }
                    }
                    return findScalar(array_info.child, ptr, end) orelse array_info.len;
                },
                else => {},
            },
            .many => if (ptr_info.sentinel()) |s| {
                if (s == end) {
                    return findSentinel(ptr_info.child, end, ptr);
                }
                // We're looking for something other than the sentinel,
                // but iterating past the sentinel would be a bug so we need
                // to check for both.
                var i: usize = 0;
                while (ptr[i] != end and ptr[i] != s) i += 1;
                return i;
            } else {
                return findSentinel(ptr_info.child, end, @ptrCast(ptr));
            },
            .c => {
                assert(ptr != null);
                return findSentinel(ptr_info.child, end, ptr);
            },
            .slice => {
                if (ptr_info.sentinel()) |s| {
                    if (s == end) {
                        return findSentinel(ptr_info.child, s, ptr);
                    }
                }
                return findScalar(ptr_info.child, ptr, end) orelse ptr.len;
            },
        },
        else => {},
    }
    @compileError("invalid type given to std.mem.sliceTo: " ++ @typeName(@TypeOf(ptr)));
}