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fantom

Dynamically evaluating code at runtime

Is it possible to take a string/AST of source code and evaluate it (like eval()) at runtime in Fantom? I found some suggesting features in the documentation but not obvious evidence.

Solution

  • It's not as easy as calling an eval() function, but it is possible. You need to first compile your Fantom code into a class before you can execute it.

    Plastic, a library from Alien-Factory, does just that. Example:

    using afPlastic

class Example {
    Void main() {
        eval("2 + 2")  // --> 4
    }

    Obj? eval(Str code) {
        model := PlasticClassModel("MyClass", true)
        model.addMethod(Obj?#, "eval", "", code)
        myType := PlasticCompiler().compileModel(model.toFantomCode)
        return myType.make->eval()
    }
}

    The PlasticCompiler class does the job of compiling Fantom code into a usable Type.

    It uses the Fantom compiler library and is based on code found in Fansh - a Fantom shell, part of the Fantom distribution.