| AngelScript

Custom options

Most applications have different needs and AngelScript is meant to be as flexible as possible to suit everybody. For this reason there are several options for customizing the script engine for the best fit.

# Registerable types

Even types that one might normally expect to be built-in to a script language, e.g. string, array, and other container classes, are registered by the application. This is to allow the application to provide the exact implementation desired.

Of course, should the application developer want to use a premade implementation the add-ons provide just that.

# Language modifications

The engine method SetEngineProperty permits making runtime choices about several different behaviours in the engine.

The following modify the script language in one way or the other:

asEP_DISALLOW_VALUE_ASSIGN_FOR_REF_TYPE

By turning on this the compiler will no longer allow the use of value assignment operators on reference types. While it may seem drastic, it can help reduce risk for bugs in the scripts, as the script writer will no longer be able to do a value assignment by mistake when he meant to a handle assignment. Reference types should usually not be copied, so the imposed restriction will likely not cause problems anyway.

asEP_ALLOW_UNSAFE_REFERENCES

By turning on unsafe references you allow in-out references to be used for primitives and value types too. Normally this will work fine, just as it does in ordinary languages such as C++, but know that it is quite possible to write scripts that will cause memory invasions or crashes if the references are not properly guarded. With this option turned on you cannot consider the scripts to be sand-boxed any longer.

asEP_USE_CHARACTER_LITERALS, asEP_ALLOW_MULTILINE_STRINGS, asEP_SCRIPT_SCANNER, asEP_STRING_ENCODING

These options are used to determine how strings are treated by the compiler. The details are described in The string type.

asEP_ALLOW_IMPLICIT_HANDLE_TYPES

This option is experimental. By turning it on script classes can be declared to always be treated as handles by declaring the class with @ before the name of the class. When this is done all variables of that type will be handles, and the assignment operator will always perform a handle assignment.

asEP_REQUIRE_ENUM_SCOPE

With this option all enum values must be prefixed with the enum type using the scope operator to qualify.

asEP_PROPERTY_ACCESSOR_MODE

Some application writers do not want to use virtual property accessors, or perhaps only wish to use them for registered types. By setting this engine property to 0 the use of property accessors is turned off completely, and setting it to 1 only registered types can be allowed to use them.

asEP_DISALLOW_GLOBAL_VARS

The application can disable the ability to declare global variables in scripts completely. This can be useful in such cases when the application wish to have full control of what can and cannot be stored by a script.

asEP_ALWAYS_IMPL_DEFAULT_CONSTRUCT

If this flag is set to true, the compiler will always provide a default constructor for classes even if it hasn't been implemented by the script. Normally this option is not recommended, because if a script class provides a non-default constructor but not the default constructor it is most likely because it is desired that the class should always be initialized with the non-default constructor.

asEP_ALTER_SYNTAX_NAMED_ARGS

If this flag is set to 1 or 2 the compiler will accept the '=' instead of ':' for naming arguments in function calls. When option 1 is used the compiler will warn about it, so the script writer can update the script to the correct ':' token. When option 2 is used both '=' and ':' are accepted silently.

Observe that the use of the '=' token for naming arguments may cause a bit of a confusion. Especially if there is a variable with the same name as the function argument as the script writer may think he's updating the value of the variable, but is just naming the function argument.

# Engine behaviours

There are also several options in SetEngineProperty for modifying the way the engine behaves.

asEP_OPTIMIZE_BYTECODE

Normally this option is only used for testing the library, but should you find that the compilation time takes too long, then it may be of interest to turn off the bytecode optimization pass by setting this option to false.

asEP_COPY_SCRIPT_SECTIONS

If wan't to spare some dynamic memory and the script sections passed to the engine is already stored somewhere in memory then you can turn off this options. If you do you'll need to be careful not to modify or deallocate the script sections until module has been built.

asEP_MAX_STACK_SIZE

The script context's stack grows dynamically as needed during executions. By default there is no limit to how large it may grow, but if you wish to set this limit you can do with this option. The limit is given in bytes, but it is only an approximate limit. Setting the limit to 1MB doesn't mean the stack will grow exactly to 1MB, but you can be certain that it will not grow much beyond that.

Whenever a context attempts to grow the stack more than it is allowed, it will abort the execution and return a 'stack overflow' script exception.

asEP_BUILD_WITHOUT_LINE_CUES

This option can be used to speed up the execution of scripts a bit. It is best described in Compile scripts without line cues.

asEP_INIT_GLOBAL_VARS_AFTER_BUILD

By default the global variables in the script modules are initialized immediately after building the scripts, but sometimes this is not desired. For example, if you debug the initialization of the variables, or if you're building an offline compiler, or even if you want to add extra validation of the variables to make sure the script doesn't declare any variables you don't want it to.

See Also
  Pre-compiled byte code

asEP_INCLUDE_JIT_INSTRUCTIONS

In order for JIT compilation to work properly it needs to have some hints in the bytecode so it can know where a switch from bytecode execution to JIT compiled execution shall be done. By default this option is turned off as it would just add an overhead to the bytecode, but when using JIT compilation this overhead will be compensated by the faster execution with direct machine code.

See Also
  How to build a JIT compiler

asEP_EXPAND_DEF_ARRAY_TO_TMPL

This option is to determine how the default array type is displayed in compiler messages and function declarations, e.g. int[] or array<int>.

asEP_AUTO_GARBAGE_COLLECT

By default AngelScript's incremental garbage collector is executed as scripts are invoked by the application. This does add a slight overhead to the execution, which is normally tolerable but in some applications the CPU cycles may be needed for other things. In this case the automatic execution of the garbage collector can be turned off to hold off on the execution until the CPU can be spared.

See Also
  Garbage collection

asEP_COMPILER_WARNINGS

Compiler warnings can be turned off or treated as errors by setting this engine property.