Method prototypes like C++? // Compiling executables

Discussion in 'Ruby' started by Claudio Freda, Feb 18, 2010.

  1. Hi, I'm switching from C++ to Ruby, I have a few questions.

    1. How come there isn't any "method prototype" feature like the function
    prototypes in C++? Like, in c++ I declared just the name of a funcion at
    the beginning of a block of code and then I could put the function
    anywhere in the program, so it could be called wherever, without
    worrying if it had been fully declared or not. Is this possible?

    2. I find it awesome that you needn't compile to view the results of
    your code; still, i would like to be able to compile my programs to an
    executable file for distribution. Is it possible?

    3. I still don't get how this whole "gems" thing work. In C++ I used to
    load libraries, it seems that in Ruby most of the libraries are loaded
    by themselves when needed. When exactly do I need to include other
    Claudio Freda, Feb 18, 2010
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  2. Sure just do it! Methods only need to exist when then are "called"
    and even then you can use the method_missing hook to define them on
    the fly if you need to.
    Look at JRuby's ability to create .class files for the JVM, but you
    might want to keep an open mind about whether you *really* need to
    It's a way to have multiple versions of libraries on your system.
    You'll know you need more because something doesn't exist. For
    example, there are some useful methods on Date that are only available
    if you "require 'date'" in your code. (Not the best example because
    that's not a gem, but a standard library, i.e., it comes as part of


    Rob Biedenharn
    Rob Biedenharn, Feb 18, 2010
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  3. [Note: parts of this message were removed to make it a legal post.]

    how to unsubscribe from this mailing list can any one please reply me.

    sandeep bupathi, Feb 18, 2010
  4. Wait, I explain my problem.
    In C++ I would have been able to to this:

    void function();
    void function() {
    cout<<"The function has been executed"

    And it would still print "The function has been executed"

    In ruby instead if I do this:

    def method; end


    def method
    print ('The method has been executed')

    it just prints me nothing; I think it has something to do with ruby's
    dynamic definitions.

    Just how to achieve the same thing in ruby? (summoning a function that
    is declared later in the code)
    Claudio Freda, Feb 18, 2010
  5. What Rob wanted to say is that you don't need to declare a function
    (method). You just call it, and it has to have been defined before the
    call. But be aware that the code inside a method is not executed when
    it's parsed, only when the method is called, so you can have this:

    irb(main):001:0> def caller
    irb(main):002:1> method("a")
    irb(main):003:1> end
    =3D> nil
    irb(main):004:0> def method(s)
    irb(main):005:1> puts s
    irb(main):006:1> end
    =3D> nil
    irb(main):007:0> caller

    You can have the definition of caller before the definition of method.
    What you can't do is call caller before defining method.

    Hope this clears up a bit,

    Jesús Gabriel y Galán, Feb 18, 2010
  6. You need that in C / C++ only because implementations are split to
    header and source files. We don't do that in Ruby. Instead, we
    implement whatever functionality we need and place it in one or more
    rb files. Those are then read by using "require".
    That's not a problem as long as execution starts later:

    def foo

    def method
    puts 'It works!'


    This is typically the case if your required files contain declarations only=
    Robert Klemme, Feb 19, 2010
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