Immutability Wastes RAM? Not Quite!

A common belief is that immutable designs waste more memory than mutable ones because every operation creates a new object. This is a misconception. The key insight is 'persistent objects': in well-designed immutable systems, operations reuse large portions of the existing object graph, only creating new objects at the top level while sharing unchanged sub-objects. Mutable designs cannot safely share object references because one owner mutating a shared object would corrupt the state of another. This means immutable designs can actually allocate fewer total objects than equivalent mutable designs, while also reducing bugs. The C# compiler is cited as a real-world example of a fast, low-memory, fully immutable system.