3.2. Modules and C++ bindings

3.2.1. Builtin modules

Builtin modules are the way to expose C++ functionality to Daslang.

Let’s look at the FIO module as an example. To create a builtin module, an application needs to do the following:

Make a C++ file where the module resides. Additionally, make a header for AOT to include.

Derive from the Module class and provide a custom module name to the constructor:

class Module_FIO : public Module {
    Module_FIO() : Module("fio") {              // this module name is ``fio``
        DAS_PROFILE_SECTION("Module_FIO");      // the profile section is there to profile module initialization time
        ModuleLibrary lib;                      // module needs library to register types and functions
        lib.addModule(this);                    // add current module to the library
        lib.addBuiltInModule();                 // make builtin functions visible to the library

Specify the AOT type and provide a prefix with C++ includes (see AOT):

virtual ModuleAotType aotRequire ( TextWriter & tw ) const override {
    tw << "#include \"Daslang/simulate/aot_builtin_fio.h\"\n";
    return ModuleAotType::cpp;

Register the module at the bottom of the C++ file using the REGISTER_MODULE or REGISTER_MODULE_IN_NAMESPACE macro:


Use the NEED_MODULE macro during application initialization before the Daslang compiler is invoked:


Its possible to have additional Daslang files that accompany the builtin module, and have them compiled at initialization time via the compileBuiltinModule function:

Module_FIO() : Module("fio") {
    // add builtin module
    compileBuiltinModule("fio.das",fio_das, sizeof(fio_das));

What happens here is that fio.das is embedded into the executable (via the XXD utility) as a string constant.

Once everything is registered in the module class constructor, it’s a good idea to verify that the module is ready for AOT via the verifyAotReady function. It’s also a good idea to verify that the builtin names are following the correct naming conventions and do not collide with keywords via the verifyBuiltinNames function:

Module_FIO() : Module("fio") {
    // lets verify all names
    uint32_t verifyFlags = uint32_t(VerifyBuiltinFlags::verifyAll);
    verifyFlags &= ~VerifyBuiltinFlags::verifyHandleTypes;  // we skip annotatins due to FILE and FStat
    // and now its aot ready

3.2.2. ModuleAotType

Modules can specify 3 different AOT options.

ModuleAotType::no_aot means that no ahead of time compilation will occur for the module, as well as any other modules which require it.

ModuleAotType::hybrid means that no ahead of time compilation will occur for the module itself. Other modules which require this one will will have AOT, but not without performance penalties.

ModuleAotType::cpp means that full blown AOT will occur. It also means that the module is required to fill in cppName for every function, field, or property. The best way to verify it is to call verifyAotReady at the end of the module constructor.

Additionally, modules need to write out a full list of required C++ includes:

virtual ModuleAotType aotRequire ( TextWriter & tw ) const override {
    tw << "#include \"Daslang/simulate/aot_builtin_fio.h\"\n"; // like this
    return ModuleAotType::cpp;

3.2.3. Builtin module constants

Constants can be exposed via the addConstant function:


The constant’s type is automatically inferred, assuming type cast infrastructure is in place (see cast).

3.2.4. Builtin module enumerations

Enumerations can be exposed via the `addEnumeration` function:


For this to work, the enumeration adapter has to be defined via the DAS_BASE_BIND_ENUM or DAS_BASE_BIND_ENUM_98 C++ preprocessor macros:

namespace Goo {
    enum class GooEnum {
    ,   hazardous

    enum GooEnum98 {
    ,   hard

DAS_BASE_BIND_ENUM(Goo::GooEnum, GooEnum, regular, hazardous)
DAS_BASE_BIND_ENUM_98(Goo::GooEnum98, GooEnum98, soft, hard)

3.2.5. Builtin module data types

Custom data types and type annotations can be exposed via the addAnnotation or addStructure functions:


See handles for more details.

3.2.6. Builtin module macros

Custom macros of different types can be added via addAnnotation, addTypeInfoMacro, addReaderMacro, addCallMacro, and such. It is strongly preferred, however, to implement macros in Daslang.

See macros for more details.

3.2.7. Builtin module functions

Functions can be exposed to the builtin module via the addExtern and addInterop routines. addExtern

addExtern exposes standard C++ functions which are not specifically designed for Daslang interop:

addExtern<DAS_BIND_FUN(builtin_fprint)>(*this, lib, "fprint", SideEffects::modifyExternal, "builtin_fprint");

Here, the builtin_fprint function is exposed to Daslang and given the name fprint. The AOT name for the function is explicitly specified to indicate that the function is AOT ready.

The side-effects of the function need to be explicitly specified (see Side-effects). It’s always safe, but inefficient, to specify SideEffects::worstDefault.

Let’s look at the exposed function in detail:

void builtin_fprint ( const FILE * f, const char * text, Context * context, LineInfoArg * at ) {
    if ( !f ) context->throw_error_at(at, "can't fprint NULL");
    if ( text ) fputs(text,(FILE *)f);

C++ code can explicitly request to be provided with a Daslang context, by adding the Context type argument. Making it last argument of the function makes context substitution transparent for Daslang code, i.e. it can simply call:

fprint(f, "boo")    // current context with be provided transparently

Daslang strings are very similar to C++ char *, however null also indicates empty string. That’s the reason the fputs only occurs if text is not null in the example above.

Let’s look at another integration example from the builtin math module:

addExtern<DAS_BIND_FUN(float4x4_translation), SimNode_ExtFuncCallAndCopyOrMove>(*this, lib, "translation",
        SideEffects::none, "float4x4_translation")->arg("xyz");

Here, the float4x4_translation function returns a ref type by value, i.e. float4x4. This needs to be indicated explicitly by specifying a templated SimNode argument for the addExtern function, which is SimNode_ExtFuncCallAndCopyOrMove.

Some functions need to return a ref type by reference:

addExtern<DAS_BIND_FUN(fooPtr2Ref),SimNode_ExtFuncCallRef>(*this, lib, "fooPtr2Ref",
    SideEffects::none, "fooPtr2Ref");

This is indicated with the SimNode_ExtFuncCallRef argument. addInterop

For some functions it may be necessary to access type information as well as non-marshalled data. Interop functions are designed specifically for that purpose.

Interop functions are of the following pattern:

vec4f your_function_name_here ( Context & context, SimNode_CallBase * call, vec4f * args )

They receive a context, calling node, and arguments. They are expected to marshal and return results, or v_zero().

addInterop exposes C++ functions, which are specifically designed around Daslang:

    builtin_read,               // function to register
    int,                        // function return type
    const FILE*,vec4f,int32_t   // function arguments in order
>(*this, lib, "_builtin_read",SideEffects::modifyExternal, "builtin_read");

The interop function registration template expects a function name as its first template argument, function return value as its second, with the rest of the arguments following.

When a function’s argument type needs to remain unspecified, an argument type of vec4f is used.

Let’s look at the exposed function in detail:

vec4f builtin_read ( Context & context, SimNode_CallBase * call, vec4f * args ) {
    DAS_ASSERT ( call->types[1]->isRef() || call->types[1]->isRefType() || call->types[1]->type==Type::tString);
    auto fp = cast<FILE *>::to(args[0]);
    if ( !fp ) context.throw_error_at(call->debugInfo, "can't read NULL");
    auto buf = cast<void *>::to(args[1]);
    auto len = cast<int32_t>::to(args[2]);
    int32_t res = (int32_t) fread(buf,1,len,fp);
    return cast<int32_t>::from(res);

Argument types can be accessed via the call->types array. Argument values and return value are marshalled via cast infrastructure (see cast).

3.2.8. Function side-effects

The Daslang compiler is very much an optimizin compiler and pays a lot of attention to functions’ side-effects.

On the C++ side, enum class SideEffects contains possible side effect combinations.

none indicates that a function is pure, i.e it has no side-effects whatsoever. A good example would be purely computational functions like cos or strlen. Daslang may choose to fold those functions at compilation time as well as completely remove them in cases where the result is not used.

Trying to register void functions with no arguments and no side-effects causes the module initialization to fail.

unsafe indicates that a function has unsafe side-effects, which can cause a panic or crash.

userScenario indicates that some other uncategorized side-effects are in works. Daslang does not optimize or fold those functions.

modifyExternal indicates that the function modifies state, external to Daslang; typically it’s some sort of C++ state.

accessExternal indicates that the function reads state, external to Daslang.

modifyArgument means that the function modifies one of its input parameters. Daslang will look into non-constant ref arguments and will assume that they may be modified during the function call.

Trying to register functions without mutable ref arguments and modifyArgument side effects causes module initialization to fail.

accessGlobal indicates that that function accesses global state, i.e. global Daslang variables or constants.

invoke indicates that the function may invoke another functions, lambdas, or blocks.

3.2.9. File access

Daslang provides machinery to specify custom file access and module name resolution.

Default file access is implemented with the FsFileAccess class.

File access needs to implement the following file and name resolution routines:

virtual das::FileInfo * getNewFileInfo(const das::string & fileName) override;
virtual ModuleInfo getModuleInfo ( const string & req, const string & from ) const override;

getNewFileInfo provides a file name to file data machinery. It returns null if the file is not found.

getModuleInfo provides a module name to file name resolution machinery. Given require string req and the module it was called from, it needs to fully resolve the module:

struct ModuleInfo {
    string  moduleName;     // name of the module (by default tail of req)
    string  fileName;       // file name, where the module is to be found
    string  importName;     // import name, i.e. module namespace (by default same as module name)

It is better to implement module resolution in Daslang itself, via a project.

3.2.10. Project

Projects need to export a module_get function, which essentially implements the default C++ getModuleInfo routine:

require strings
require daslib/strings_boost

    module_info = tuple<string;string;string> const // mirror of C++ ModuleInfo

def module_get(req,from:string) : module_info
    let rs <- split_by_chars(req,"./")                  // split request
    var fr <- split_by_chars(from,"/")
    let mod_name = rs[length(rs)-1]
    if length(fr)==0                                    // relative to local
        return [[auto mod_name, req + ".das", ""]]
    elif length(fr)==1 && fr[0]=="daslib"               // process `daslib` prefix
        return [[auto mod_name, "{get_das_root()}/daslib/{req}.das", ""]]
        for se in rs
        let path_name = join(fr,"/") + ".das"           // treat as local path
        return [[auto mod_name, path_name, ""]]

The implementation above splits the require string and looks for recognized prefixes. If a module is requested from another module, parent module prefixes are used. If the root daslib prefix is recognized, modules are looked for from the get_das_root path. Otherwise, the request is treated as local path.