Read-only Strings [Advanced]

Strings in SB can be writable or read-only (Note that this applies to /values/, not /variables/) Read-only strings don't use any memory (as measured by FREEMEM), and I suspect that their data pointers point to immediate string data in the bytecode, rather than data in user memory like normal strings. * Creating read-only strings A read-only string value is created whenever a constant string expression is passed to a function. String arrays also start out filled with empty read-only strings. All other string values which you can access (as far as I know) will be writable. There is no way to convert an arbitrary writable string into a read-only string at runtime, though there would be (as far as I know) no advantage to doing this. ``` TEST "ABC" 'parameter S will contain a read-only string DEF TEST S ... END DIM S$[10] 'S$ is filled with read-only strings (with value "") ``` * Converting read-only strings to writable strings - if the value passed to FILL is read-only, the array will be filled with a writable copy. In these situations, the string value will be re-allocated: - using INC, SWAP, = on a variable containing a read-only string - assigning to an index in a variable containing a read-only string - using PUSH or UNSHIFT on a read-only string Anyway, under most circumstances, read-only strings will not cause problems. Trying to modify them will just replace them with a copy, rather than failing. However, there are places where they act differently from normal strings: ``` DEF TEST S VAR A=S,B=S INC A,"D" ?A,B END ``` if you pass a normal, writiable string value, this behaves as expected. S and T store references to the same string value, so modifying it affects both variables. ``` A="ABC" TEST A 'prints: ABCD ABCD ``` However, passing a read-only string is different: ``` TEST "ABC" 'prints ABCD ABC ``` This is because, each time the read-only string is assigned, it creates a copy. So, S and T's values will be different strings. (this also means that, ironically, read-only strings can be slower because they need to be copied each time they are assigned to something)