Is it allowed in programming to modify the state of data inside a method intended only for reading?

In programming, a method intended only for reading (for example, marked as const in C++ or a method without side effects) should not modify the state of the object or data it has access to. This is important for ensuring predictability and safety of the code.

However, technically in some languages it is possible to change the state inside such a method (for example, through mutable fields or bypassing restrictions), but this is considered bad practice and violates the method's contract.

In conclusion: modifying the state of data inside a method intended only for reading is not recommended and is usually prohibited by language rules or conventions to avoid unexpected side effects.