In addition to var parameters and normal parameters (call by value, call by reference), Free Pascal also supports Const parameters. You can specify a Const parameter as follows:
Function Name (Const S: Type_Of_S) : ResultTypeA constant argument is passed by refenence (i.e. the function or procedure receives a pointer to the passed , but you are not allowed to assign to it, this will result in a compiler error.
The main use for this is reducing the stack size, hence improving performance.