mono/doc/faq

** Basics

Q: Is Mono the same as Microsoft's .NET initiative?

A: It is not. 

   .NET is a company-wide initiative at Microsoft that
   encompasses many different areas. The .NET development framework,
   Passport, Biztalk, new server products, and anything that is
   remotely connected to .NET gets the ".NET-stamping" treatment.
   Some components of Microsoft's .NET initiative have been announced
   and some others are in the works.

  Mono is a project to implement several technologies developed by
   Microsoft that have now been submitted to the ECMA Standards Body.   

Q: What technologies are included in Mono?

A: Mono contains a number of components useful for building new
   software:

	<ul>
		* A Common Language Infrastructure (CLI) virtual
		  machine that contains a class loader, Just-in-time
		  compiler, and a garbage collecting runtime.

		* A class library that can work with any language
		  which works on the CLR.

		* A compiler for the C# language.  In the future we
		  might work on other compilers that target the Common
		  Language Runtime.

		  Windows has compilers that target the
		  virtual machine from
		  <a href="http://msdn.microsoft.com/net/thirdparty/default.asp#lang">a
		  number of languages:</a> Managed C++, Java Script,
		  Eiffel, Component Pascal, APL, Cobol, Oberon, Perl,
		  Python, Scheme, Smalltalk, Standard ML, Haskell,
		  Mercury and Oberon.
	</ul>

   The CLR and the Common Type System (CTS) enables applications and
   libraries to be written in a number of languages.  Classes and
   methods created in one language can be used from a different
   language. 

   This means for example that if you define a class to do algebraic
   manipulation in C#, that class can be reused from any other
   language that supports the CLI.  You could create a class in C#,
   subclass it in C++ and instantiate it in an Eiffel program. 

   A single object system, threading system, class libraries, and
   garbage collection system can be shared across all these languages.
   
Q: Where can I find the specification for these technologies?

A: You can find the work-in-progress documentation from the T3G ECMA
   group here:
 
   <a href="http://www.dotnetexperts.com">http://www.dotnetexperts.com</a>

Q: Will you implement the .NET Framework SDK class libraries?

A: Yes, we will be implementing the APIs of the .NET Framework SDK
   class libraries. 

Q: What does Mono stand for?

A: Mono is the word for `Monkey' in Spanish. We like monkeys.

   It only means a number of other things: monochromatic (hence the
   gray theme used in the Web site).

Q: When will you ship it?

A: We do not know when the code will be shipped.  The more
   contributions we get to the project, the sooner it will ship.

   A rough estimate is that we might be able to run our C# compiler on
   Linux by the end of the year.  That means running the Windows
   Executable generated by a Microsoft .NET compiler on the Linux
   platform.

   We expect that doing GUI applications will require more work on the
   class libraries. That could take another six months.

Q: How can I contribute?

A: Check the <a href="contributing.html">contributing</a> section. 

Q: You guys should innovate instead of copying.

A: In this particular case, we see a clear advantage in the platform
   and we are interested in using the features of the CLI on open source systems.

   We have decided that we should spend our limited resources towards
   implementing an existing specification instead of designing and
   implementing our own.

   Designing and implementing our own would be possible, but it doesn't make
   sense to do that just because the specification comes from a
   proprietary vendor.  

** Ximian

Q: Why is Ximian working on .NET?

A: We are interested in providing the best tools for programmers to
   develop applications for Free Operating Systems.  

   For more information, read the project <a
   href="rationale.html">rationale</a> page.

Q: Will Ximian be able to take on a project of this size?  

A: Ximian will not be able to taken on the whole project on its own.
   Mono will be a free software/open source community project, that is
   the only way we can hope to implement something of this size.  You
   can <a href="contributing.html">contribute</a> to this effort.

Q: What pieces will Ximian be working on?

A: We will focus on building a development and execution
   environment.  

   The idea is to get Mono to a state of that would allow
   third parties to actually be able to use it real-world development.

Q: Why does Ximian even care?

A: We like the features that the CLI and its related technologies
   bring to the table.  An exciting addition to the developer toolkit.
   The goal of Mono is to bring this technology to non-Windows
   platforms (although we hope Mono will also run on Windows, for
   debugging and comparative purposes).


** Licensing

Q: Will I be able to write proprietary applications that run with
   Mono?

A: Yes.  The licensing scheme is planned to allow proprietary
   developers to write applications with Mono.
   
Q: What license is Mono on?

A: The C# Compiler is released under the terms of the GPL.  The class
   libraries will be under the LGPL or the GPL with a special
   exception.  The runtime libraries are under the LGPL.

   Since the LGPL is not suitable for embedded systems development, we
   are also licensing the libraries under the GPL with the following exception:

   If you link this library against your own program, then you do not
   need to release the source code for that program. However, any
   changes that you make to the library itself, or to any native
   methods upon which the library relies, must be re-distributed in
   accordance with the terms of the GPL.

   This is similar in spirit to <a
   href="http://www.gnu.org/software/classpath/classpath.html">GNU
   Classpath.</a>

Q: But in Object Oriented Programming I need to subclass your library
   functions, does that mean that I am making modifications to your
   library and hence I would have to distribute my sources under the
   LGPL?

A: No.  Object Oriented Programming in the class library is a well
   understood interface barrier, so you can actually develop
   proprietary applications with the Mono libraries. 

Q: Will you accept code under the XXX License?

A: If the XXX License is compatible with the license we use in that
   specific piece of code, then yes.  If you want to use the BSD license, make
   sure you use the BSD license without the advertisement clause (The
   `Ousterhout License').

** Mono and .NET

Q: If applications use Mono, does that mean that I have to pay a service fee?

A: No.  Mono is not related to Microsoft's initiative of
   software-as-a-service. 

Q: If you implement .NET, will I depend on Microsoft Passport to run my software?

A: No.  The .NET Framework is a runtime infrastructure and collection
   of class libraries.  Passport may be required to access certain web
   services written for that framework, but only if the programmer
   chooses Passport as the authentication mechanism.

Q: Is .NET just a bunch of marketing slogans?

A: Although the `.NET initiative' is still quite nebulous, The .NET Framework
   has been available for some time.  Mono is not an implementation of the .NET
   initiative, just the development framework.

Q: What is a 100% .NET application?

A: A `100% .NET application' is one that only uses the APIs defined
   under the System namespace and does not use PInvoke.  These
   applications would in theory run unmodified on Windows, Linux,
   HP-UX, Solaris, MacOS X and others. 

Q: But Microsoft will release a port of the real thing under the
   `Shared Source' license, why bother with anything else?

A: The Shared Source implementation will not be usable for commercial
   purposes.  We are working towards an implementation that will grant
   a number of rights to recipients: use for any purpose,
   redistribution, modification, and redistribution of modifications.

   This is what we call <a
   href="http://www.gnu.org/philosophy/free-sw.html">Free Software</a>

** Passport

Q: Is this a free implementation of Passport?

A: No.  Passport is part of Microsoft's Hailstorm initiative.  Mono
   is just a runtime, a compiler and a set of class libraries. 

Q: Will the System.Web.Security.PassportIdentity class, mean
   that my software will depend on Passport?
   
A: No.  That just means that applications might use that API to
   contact a Passport site.  

   As long as your application does not use Passport, you will not
   need Passport.  

   It might even be possible to implement that class with
   a set of dummy functions, or use an alternate Passport implementation.

   We do not know at this time whether the Passport protocol is
   documented and whether we will be able to talk to
   passport.com 

Q: But that must mean that you are tied to Passport!

A: All the contrary.  The implementation could keep the interface (for
   the sake of simplicity, lets say it implements the method `Login'
   and `GetUserName').

   We could implement `Login' and `GetUserName' by talking to XNS or
   any other decentralized systems.  Or any other system that the
   industry standarizes on.

Q: What is your opinion?

A: You can read my personal <a href="passport.html">opinion on
   passport</a>.

Q: Will Mono running on Linux make Passport available for Linux?

A: The Passport toolkit for Linux-based web servers is available from
   Microsoft.  

   Again, Mono has nothing to do with Passport. 

** Mono and Windows

Q: Will Mono allow me to run Microsoft Office on Linux?

A: No, it will not.  Microsoft Office is a Windows application.  To
   run Windows applications on Intel Unix systems refer to <a
   href="http://www.winehq.com">the Wine Project</a>

** GNOME

Q: How is this related to GNOME?

A: In a number of ways:

	* Mono will use existing
	  components that have been developed for GNOME when it makes
	  sense.  For example on X systems, we will use Gtk+ and
          Libart to implement Winforms and the Drawing2D API.  

	  For database access, we will use LibGDA (not really
          depending on GNOME, but related to).

	* This project was born out of the need of providing improved
	  tools for the GNOME community. 

	* We would like to add support to our CLR implementation to
	  deal with GObjects (in GNOME 1.x, they are called
	  GtkObjects), and allow Mono developers to provide GObjects
	  or use and extend existing GObjects.

Q: Has the GNOME Foundation or the GNOME team adopted Mono?

A: Mono is too new to be adopted by those groups. We hope that the
   tools that we will provide will be adopted by free software
   programmers including the GNOME Foundation members and the GNOME
   project generally.

Q: Should GNOME programmers switch over to Mono?

A: Mono will not be ready even within the next six months, and a
   complete implementation is probably one year away.  

   We encourage GNOME developers to continue using the existing tools,
   libraries and components.  Improvements made to GNOME will have an
   impact on Mono, as they will provide the "backend" for various
   classes. 

Q: Will Mono include compatibility with Bonobo components?

A: Yes, we will provide a set of classes for implementing and using
   Bonobo components from within Mono. 

Q: Does Mono replace Bonobo?

A: Bonobo is very focused on cross-application component reuse.  Mono
   will provide a Bonobo framework to allow you to develop Bonobo
   components and use Bonobo components on Unix.  

   Mono should allow you to write Bonobo components more easily, just
   like .NET on Windows allows you to export .NET components to COM.

** Mono and the Web

Q: Is Mono a way of running Java applets?

A: No.

** Web Services

Q: Is Mono just a new way of writing Web Services?

A: No.

Q: If this implements the SDK classes, will I be able to write and
   execute .NET Web Services with this?
   
A: Yes, you will.

   When the project is finished, you will be able to use the same
   technologies that are available through the .NET Framework SDK on
   Windows to write Web Services.

Q: What about Soup?

A: Soup is a library for GNOME applications to create SOAP server and
   SOAP clients.   You can browse the source code for soup using <a
   href="http://cvs.gnome.org/bonsai">GNOME's Bonsai</a>

Q: Can I use CORBA?

A: Yes. The CLI contains enough information about a class that
   exposing it to other RPC systems (like CORBA) is really simple, and
   does not even require support from an object.  

   We will be implementing CORBA interoperation as an extension to the
   Mono classes so that we can integrate with Bonobo, just like
   Microsoft provides COM interoperation classes and support
   mechanisms. 

Q: Can I serialize my objects to other things other than XML?

A: Yes, although the serializing tools have not yet been planned, and
you would probably have to implement them yourself.

** Development Tools 

Q: Will it be possible to use the CLI features without using bytecodes
   or the JIT?

A: Yes. The CLI engine will be made available as a shared library.
   The garbage collection engine, the threading abstraction, the
   object system, the dynamic type code system and the JIT will be
   available for C developers to integreate with their applications if
   they wish to do so. 

Q: Will you have new development tools?

A: Hopefully Free Software enthusiasts will contribute tools to
   improve the developer environment.  These tools could be developed
   initially using Microsoft implementation of the CLI and then
   executed later with Mono.

** Mono and Java
   
Q: What about using Java?  After all there are many languages that
   target the Java VM.

A: You can get very good tools for doing Java development on free
   systems right now.  <a href="http://www.redhat.com">Red Hat</a> has
   contributed a <a href="http://gcc.gnu.org">GCC</a> <a
   href="http://gcc.gnu.org/java">frontend for Java</a> that can take
   Java sources or Java byte codes and generate native executables; <a
   href="http://www.transvirtual.com">Transvirtual</a> has implemented
   <a href="http://www.kaffe.org">Kaffe</a> a JIT engine for Java;
   Intel also has a Java VM called <a
   href="http://www.intel.com/research/mrl/orp">ORP</a>.

   The JVM is not designed to be a general purpose virtual machine.
   The Common Intermediate Language (CIL), on the other hand, is
   designed to be a target for a
   wide variety of programming languages, and has a set of rules
   designed to be optimal for JITers.


Q: What kind of rules make the Common Intermediate Language useful for
   JITers?

A: The main rule is that the stack in the CLI is not a general purpose
   stack.   You are not allowed to use it for other purposes than
   computing values and passing arguments to functions or return
   values.  

   At any given call or return instruction, the types on the stack
   have to be the same independently of the flow of execution of your
   code. 

Q: I heard that the CIL is ideal for JITing and not efficient for
   interpreters, is this the case?

A: The CIL is better suited to be JITed than JVM byte codes, but you
   can interpret them as trivially as you can interpret JVM byte
   codes. 

Q: Could Java target the CLI?

A: Yes, Java could target the CLI.  We have details on a <a
   href="ideas.html#guavac">project</a> that someone could take on to
   make this happen.

** Extending Mono

Q: Would you allow other classes other than those in the
   specification?

A: Yes.  The Microsoft class collection is very big, but it is by no
   means complete.  It would be nice to have a port of `Camel' (the
   Mail API used by Evolution inspired by Java Mail) for Mono
   applications.  

   You might also want to look into implementing CORBA for Mono.  Not
   only because it would be useful, but because it sounds like a fun
   thing to do, given the fact that the CLI is such a type rich
   system. 

   For more information on extending Mono, see our <a
   href="ideas.html">ideas</a> page.

** Mono and portability

Q: Will Mono only work on Linux?

A: Currently, we are doing our work on Linux-based systems and
   Windows.  We do not expect many Linux-isms in the code, so it
   should be easy to port Mono to other UNIX variants.   

Q: What about Mono on non X-based systems?

A: Our main intention at Ximian is to be able to develop GNOME
   applications with Mono, but if you are interested in providing a
   port of the Winform classes to other platforms (frame buffer or
   MacOS X for example), we would gladly integrate them, as long
   they are under a Free Software License. 

** Reusing existing Code

Q: What projects will you reuse or build upon?

A: We want to get Mono in the hands of programmers soon.  We are
   interested in reusing existing open source software.

Q: What about Intel's research JIT framework, ORP?

A: At this time, we are investigating whether we can use elements of
   ORP for Mono.   ORP is a research JIT engine that has a clear
   defined API that splits the JIT from the GC system and the actual
   byte code implementation.   It is a research product.

Q: What about using GNU Lightning?

A: We are also researching <a
   href="http://www.gnu.org/software/lightning/lightning.html">GNU
   Lightning</a>.

<a name="ximian-and-microsoft">
** Ximian and Microsoft

Q: I read that Microsoft is helping out Ximian, is this true?

A: Initial contact between David Stutz and Miguel de Icaza happened.
   It was a friendly conversation.  Microsoft is interested in other
   implementing .NET and are willing to help make the ECMA spec more
   accurate for this purpose.

   We were initially contacted by Sam Ruby at the ECMA TG3 committee
   to discuss the same issue.  And we are glad to have good contacts
   to ask questions about the specs. 

Q: Is Microsoft paying Ximian to do this?

A: No, we are doing this for purely selfish reasons.  We are upgrading
   our development platform to build better applications on Unix and other
   systems.

Q: Do you fear that Microsoft will change the spec and render Mono useless?

A: No.  Microsoft proved with the CLI and the C# language that it was
   possible to create a powerful foundation for many languages to
   interoperate.  We will always have that.  

   Even if changes happened in the platform which were undocumented
   (which is very unlikely), the existing platform has a value on its
   own.

   Miguel once explained its motivation for working on Mono to Dave
   Winer, and his mail got posted <a
   href="http://scriptingnews.userland.com/stories/storyReader$1275">here</a>

Q: Didn't Miguel de Icaza say that `Unix Sucks'?

A: Yes, he did, as a catch phrase in his opening remark on the Ottawa
   Linux Symposium.  His talk focused on various ways to improve Unix.

   There is a paper describing some ways to improve Unix at:

	<a href="http://primates.ximian.com/~miguel/bongo-bong.html">
        http://primates.ximian.com/~miguel/bongo-bong.html</a>

Q: Didn't Ximian's Miguel work for Microsoft?

A: Actually, Nat Friedman (Ximian's co-founder) did work as an
   intern for Microsoft for one summer but Miguel did not.

Q: Did Nat and Miguel meet at Microsoft?

A: They met online on the Linux IRC network;  They met in person for
   the first time in 1997.

** Mono and Microsoft
   
Q: How can you expect Mono to compete with Microsoft, wont this
   require an effort too large?

A: You are right.  Mono will never become a reality without the help
   of other contributors.  Ximian is a small company that can not
   finish Mono alone.  We will be working with members of the
   community to deliver the product.

Q: Is Microsoft and Corel involved in the Mono implementation?

A: No, they are not.

Q: Are you writing Mono from the ECMA specs?

A: yes, we are writing them from the ECMA specs and the published
   materials in print about .NET

Q: What happens if Microsoft `Embraces and Extends' the CLI standard
   and keeps Mono out of the play?

A: There are various explanations to this question.  The first one is
   that the benefits that you can get from the CLI are going to be
   there with or without `embracing and extending'.  We might not be
   able to run every .NET Windows application on Mono.  But remember:
   it was already easy for someone to just use PInvoke to tie their
   application to Windows.

   The bottom line is that the advantages of having a CLI runtime will
   be with us, no matter if Microsoft forks their version to be
   incompatible. 

Q: What if Microsoft changes the interface, and all of a sudden 
   applications break?

A: If they change their released API, every application that was
   developed against it will break.  

   That being said, Microsoft have a pretty good record of keeping
   backwards binary compatibility.

** Acronyms

Q: What is the difference between CLR (Common Language Runtime) and
   CLI (Common Language Infrastructure)?

A: CLI is the specification of an execution system.  The Microsoft
   implementation of this specification is named CLR. 

   Unless we come up with our own acronym, we could just call ours
   also CLR, just because it would do exactly the same thing the
   Microsoft implementation does.

<a name="gcc">
** Mono and GCC

Q: Should someone work on a GCC front-end to C#?

A: I would love if someone does, and we would love to help anyone that
   takes on that task, but we do not have the time or expertise to
   build a C# compiler with the GCC engine.  I find it a lot more fun
   personally to work on C# on a C# compiler, which has an intrinsic
   beauty.

   We can provide help and assistance to anyone who would like to work
   on this task.

Q: Should someone make a GCC backend that will generate CIL images?

A: I would love to see a backend to GCC that generates CIL images.  It
   would provide a ton of free compilers that would generate CIL
   code.  This is something that people would want to look into
   anyways for Windows interoperation in the future.

   Again, we would love to provide help and assistance to anyone
   interested in working in such a project.

Q: What about making a front-end to GCC that takes CIL images and
   generates native code?

A: I would love to see this, specially since GCC supports this same
   feature for Java Byte Codes.  You could use the metadata library
   from Mono to read the byte codes (ie, this would be your
   "front-end") and generate the trees that get passed to the
   optimizer.

   Ideally our implementation of the CLI will be available as a shared
   library that could be linked with your application as its runtime
   support. 

   Again, we would love to provide help and assistance to anyone
   interested in working in such a project.
   
Q: But would this work around the GPL in the GCC compiler and allow
   people to work on non-free front-ends?

A: People can already do this by targeting the JVM byte codes (there
   are about 130 compilers for various languages that target the JVM).

Q: Why are you writing a JIT engine instead of a front-end to GCC?

A: The JIT engine and runtime engine will be able to execute CIL
   executables generated on Windows.

** Mono and Portability

Q: Will Mono work on other variants of Unix?

A: Yes.  We do not expect to add any gratuitous incompatibilities.

Q: Will Mono run on Windows?

A: Hopefully yes.  Currently some parts of Mono only run on Windows
   (the C# compiler is a .NET executable) and other parts have only
   been compiled on Linux, but work on Windows with Cygwin.

Q: Will Mono depend on GNOME?

A: It will depend only if you are using a particular assembly (for
   example, for doing GUI applications).  If you are just interested
   in Mono for implementing a `Hello World Enterprise P2P Web
   Service', you will not need any GNOME component.

** Performance

Q: How fast will be Mono?

A: We can not predict the future, but a conservative estimate is that
   it would be at least `as fast as other JIT engines'.

   Now, wishfully thinking I hope that we will ship various JITs with
   Mono just like Microsoft has done.  A fast JITer when maximum
   performance is not needed, but fast load times are important;  And
   an optimizing JITer that would be slower at generating code but
   produce more optimal output.

   The CIL has some advantages over the Java byte code:  it is really
   an intermediate representation and there are a number of
   restrictions on how you can emit CIL code that simplify creating
   better JIT engines.

   For example, on the CIL the stack is not really an abstraction
   available for the code generator to use at will: it is just a way
   of creating a postfix representation of the parsed tree.  At any
   given call point or return point, the contents of the stack are
   expected to contain the same object types independently of how the
   instructions was reached.


** Mono and Portable.NET

Q: What are the differences between Mono and Portable.NET?

A: Most of Mono is being written using C#, the only pieces written in
   C are those who have to absolutely be built using C (The JIT
   engine, the runtime, the interfaces to the garbage collection
   system).

   The C# compiler and the tools will become reusable C# components.

   Portable.NET is building its components out of C pieces.

** Assorted questions

Q: You say that the CLI allows multiple languages to execute on the
   same environment.  Isn't this the purpose of CORBA?

A: The key difference between CORBA (and COM) and the CLI is that the
   CLI allows "data-level interoperability" because every
   language/component uses the same data layout and memory management.

   This means you can operate directly upon the datatypes that someone
   else provides, without having to go via their interfaces.  It also
   means you don't have to "marshall" (convert) parameters (data
   layouts are the same, so you can just pass components directly) and
   you don't have to worry about memory managment, because all
   languages/components share the same garbage collector and address
   space.  This means much less copying and no need for reference
   counting.