Method ExprCalc

tutorials/integration/cpp/18_dynamic_scripts.cpp:43–107

Compile the expression into a tiny daslang program. Each variable becomes a global "var name = 0.0f". A single [export] function "eval" returns the expression result.

// Each variable becomes a global "var name = 0.0f".
// A single [export] function "eval" returns the expression result.
ExprCalc::ExprCalc(const string & expr, const ExprVars & vars) {
    TextWriter ss;
    // gen2 syntax — use options gen2 and require math for trig/sqrt/etc.
    ss << "options gen2\n";
    ss << "require math\n\n";
    // Declare each variable as a module-level global.
    for (auto & v : vars) {
        ss << "var " << v.first << " = 0.0f\n";
    }
    // The evaluator function simply returns the expression.
    ss << "\n[export]\n"
       << "def eval() : float {\n"
       << "    return " << expr << "\n"
       << "}\n"
       << "\n";
    string text = ss.str();

    // --- Register the source string as a virtual file ---
    //
    // TextFileInfo wraps a raw character buffer.  setFileInfo tells the
    // file-access layer that "expr.das" resolves to this buffer instead
    // of a real file on disk.
    TextPrinter tout;
    auto fAccess = make_smart<FsFileAccess>();
    auto fileInfo = make_unique<TextFileInfo>(text.c_str(),
                                             uint32_t(text.length()), false);
    fAccess->setFileInfo("expr.das", das::move(fileInfo));

    // --- Compile the virtual file ---
    ModuleGroup dummyLibGroup;
    auto program = compileDaScript("expr.das", fAccess, tout, dummyLibGroup);
    if (program->failed()) {
        tout << "Compilation failed:\n";
        for (auto & err : program->errors) {
            tout << reportError(err.at, err.what, err.extra,
                                err.fixme, err.cerr);
        }
        return;
    }

    // --- Simulate into a shared context ---
    ctx = make_shared<Context>(program->getContextStackSize());
    if (!program->simulate(*ctx, tout)) {
        tout << "Simulation failed:\n";
        for (auto & err : program->errors) {
            tout << reportError(err.at, err.what, err.extra,
                                err.fixme, err.cerr);
        }
        return;
    }

    // --- Look up the function ---
    fni = ctx->findFunction("eval");

    // --- Map each variable name to its address in context memory ---
    //
    // findVariable returns -1 if not found; getVariable returns a raw
    // pointer into the context's global-variable segment.