Don't crash on printing nested types

When adding an Array or Dictionary to itself operator String() got in an
infinite loop. This commit adds a stack to operator String() (Through
the use of a new 'stringify method'). This stack keeps track of all
unique Arrays and Dictionaries it has seen. When a duplicate is found
only a static string is printed '[...]' or '{...}'.

This mirror Python's behavior in a similar case.

1 files changed, 2 insertions, 0 deletions

diff --git a/core/array.h b/core/array.h
index 6158db4065..d4e937a486 100644
--- a/core/array.h
+++ b/core/array.h
@@ -94,6 +94,8 @@ public:
 	Variant min() const;
 	Variant max() const;
 
+	const void *id() const;
+
 	Array(const Array &p_from);
 	Array();
 	~Array();