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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_EMPTY_LIST_ELEMENTS

By turning on this option the compiler will no longer accept empty list elements in initialization lists. The following will for example not be supported:

      array<int> arr = {1,2,,4,5,};

When not turned on, the compiler will leave the empty list elements with the uninitialized value, just as an uninitialized variable of the same type.

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 Custom string type.

asEP_HEREDOC_TRIM_MODE

With this option the compiler can be set to always trim heredoc strings, only trim if it is multiple lines, or never trim them.

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

By default virtual property accessors when declared as individual functions need to be marked as such with the keyword 'property', or else the compiler won't consider the functions as virtual properties. This behaviour was introduced in version 2.33.1.

Before this version, the compiler would automatically identify functions with the pre-fix 'get_' or 'set_' as virtual property accessors if the function signature was appropriate. This led to undesired behaviour when developers would declare such functions without the intention of them being used as virtual properties and yet the compiler used them as such.

For backwards compatibility it is still possible to configure the engine to use this behaviour by setting the engine property asEP_PROPERTY_ACCESSOR_MODE to 2.

If it also possible to disable virtual property accessors all together by setting the engine property to 0. Setting the option to 1 only allows virtual property accessors for registered functions, but still without requiring the keyword 'property'.

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.

asEP_DISABLE_INTEGER_DIVISION

This option changes the default behaviour of the / and /= operators. When true, this option replaces integer division with floating-point division, e.g. 1/2 == 0.5 instead of 1/2 == 0

asEP_PRIVATE_PROP_AS_PROTECTED

When this option is set to true the compiler will not prevent the access to private properties inherited from the parent class. It will only write a warning.

This option is provided to give backwards compatibility for scripts written between versions 2.19.1, when support for private properties was added, albeit working more like protected properties, and version 2.30.0 when the behaviour was changed so that private properties work like in other languages, i.e. they can't be accessed by derived classes.

asEP_ALLOW_UNICODE_IDENTIFIERS

When this option is set to true the compiler will accept identifiers that contain characters with byte value higher than 127. This permits the use of international characters in the identifiers as the script can be encoded in UTF-8 format and compiler normally.

# Engine behaviours

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

asEP_MAX_NESTED_CALLS

This property defines how many recursive nested calls the engine should accept. In this context a nested call is when a script calls into an application registered function that in turn calls another script function. The second call is then said to be a nested call.

By default the engine will accept 100 nested calls.

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 you want 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, asEP_INIT_STACK_SIZE, asEP_MAX_CALL_STACK_SIZE, asEP_INIT_CALL_STACK_SIZE

The script context's data 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 the asEP_MAX_STACK_SIZE 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.

Similarly the call stack also grows dynamically as needed during executions. The default here is also no limit, with the ability to limit maximum size by setting the asEP_MAX_CALL_STACK_SIZE. This limit is set in number of function calls.

In some cases it may be useful to set the initial stack size too, e.g. if you know beforehand that a large stack is needed, or if you wish to avoid any runtime memory allocations during an execution. In this case you can use the asEP_INIT_STACK_SIZE for the data stack, and asEP_INIT_CALL_STACK_SIZE for the call stack.

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.

asEP_GENERIC_CALL_MODE

By default the generic calling convention treats the ref counts in the handles the same way that the native calling convention, i.e. releases any handles passed to a function if they have been marked as auto handles, and increments the returned handle if it has been marked as auto handle.

If the behaviour used before 2.33.0 is desired for backwards compatibility, then set this property to 0. In this case the generic calling convention will always release references for handles received in arguments, and never increment references for returned handles.