Restrictions of C++ Language Features

Qubic enforces strict coding rules to ensure determinism, security, and network-wide consistency. Below is a list of forbidden language features and why they are restricted:

Prohibited Feature	Reason
Local variables on the stack	Avoids nondeterministic memory layouts. Use _WITH_LOCALS macros or store data in contract state.
Pointers (*, casting, dereferencing)	Unsafe and non-deterministic. Only allowed for multiplication.
Array brackets ([ ])	Prevents unchecked buffer access and low-level arrays, which can lead to memory issues.
Preprocessor directives (#)	Disallowed to avoid hidden logic and platform-specific behavior. #include "qpi.h" is allowed only temporarily for IntelliSense.
Floating-point types (float, double)	Arithmetic is not deterministic across platforms.
Division (/) and modulo (%)	Division by zero may cause inconsistent behavior. Use div() and mod() instead, which return 0 safely.
Strings (") and chars (')`	Can lead to memory access violations or random memory jumps.
Variadic arguments (...)	Compiler-dependent and unsafe for auditing.
Double underscores (__)	Reserved for internal use; may conflict with system symbols.
QpiContext, const_cast	Can be misused to alter internal contract behavior.
Scope resolution (::)	Only allowed for structs, enums, and namespaces inside contracts or qpi.h.
typedef, union	Reduces code clarity and may be used to obscure logic or manipulate memory.
Global variables	Disallowed to avoid shared mutable state. Global constants must be prefixed with the contract state struct name.
Recursion / deep call nesting	Limited to 10 levels to ensure execution is bounded and safe.
Complex types in input/output	Only simple types (sint, uint, bit, id, Array, BitArray) are allowed. Complex types like Collection are banned to ensure consistent state.