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    <p>For the moment, let's consider Linux.</p> <p>For Linux, the first two points tend to have relatively low relevance. Most software is open source, and many users are accustomed to building from source in any case. For such users, binary compatibility/reuse is of little or no consequence (in fact, quite a few users are likely to reject all software that isn't distributed in source code form).</p> <p>Being able to load and run (with reduced capabilities) when a component is missing is also most often a closed-source problem. Closed source software typically has several versions with varying capabilities to support different prices. It's convenient for the vendor to be able to build one version of the main application, and give varying levels of functionality depending on which other components are supplied/omitted.</p> <p>That's primarily to support different price levels though. When the software is free, there's only one price and one version: the <a href="http://www.codinghorror.com/blog/2009/07/oh-you-wanted-awesome-edition.html" rel="noreferrer">awesome edition</a>.</p> <p>Access to library functionality between languages again tends to be based more on source code instead of a binary interface, such as using <a href="http://www.swig.org/" rel="noreferrer">SWIG</a> to allow use of C or C++ source code from languages like Python and Ruby. Again, COM is basically curing a problem that arises primarily from lack of source code; when using open source software, the problem simply doesn't arise to start with.</p> <p>Low-overhead RPC to code in other processes again seems to stem primarily from closed source software. When/if you want Microsoft Excel to be able to use some internal "stuff" in, say, Adobe Photoshop, you use COM to let them communicate. That adds run-time overhead <em>and</em> extra complexity, but when one of the pieces of code is owned by Microsoft and the other by Adobe, it's pretty much what you're stuck with.</p> <p>In open source software, however, if project A has some functionality that's useful in project B, what you're likely to see is (at most) a fork of project A to turn that functionality into a library, which is then linked into both the remainder of project A and into Project B, and quite possibly projects C, D, and E as well--all without imposing the overhead of COM, cross-procedure RPC, etc.</p> <p>Now, don't get me wrong: I'm not trying to act as a spokesperson for open source software, nor to say that closed source is terrible and open source is always dramatically superior. What I <em>am</em> saying is that COM is defined primarily at a binary level, but for open source software, people tend to deal more with source code instead.</p> <p>Edit: I should probably add that SWIG was only one example among several of tools that support cross-language development at a source-code level. While SWIG is widely used, COM is different from it in one rather crucial way: with COM, you define an interface in a single, neutral language, and then generate a set of language bindings (proxies and stubs) that fit that interface. This is rather different from SWIG, where you're matching directly from one source to one target language (e.g., bindings to use a C library from Python).</p> <p>In the open source world there are also tools to define an interface in a neutral interface definition language, then generate bindings for specific languages from that interface definition. CORBA is well known, but generally viewed as large and complex, so actual use is fairly minimal. <a href="http://thrift.apache.org/" rel="noreferrer">Apache Thrift</a> provides some of the same general type of capabilities, but in a rather simpler, lighter-weight fashion. In particular, where CORBA attempts to provide a complete set of tools for distributed computing (complete with everything from authentication to distributed time keeping), Thrift follows the Unix philosophy much more closely, attempting to meet exactly one need: generate proxies and stubs from an interface definition (written in a neutral language). If you <em>want</em> to do those CORBA-like things with Thrift you undoubtedly can, but in a more typical case of building internal infrastructure where the caller and callee trust each other, you can avoid a lot of overhead and just get on with the business at hand.</p>
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    1. COInteresting perspective.
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      1. USLen Holgate
    2. COThe advantage of a shared standard like COM over things like SWIG and JNI is that it's an O(N) solution instead of an O(N*N) solution, given N languages. (That's actually unrelated to source vs binary)
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    3. COThat's really interesting, the whole open/closed source aspect wasn't mentioned in any of the COM reading I've done so far and it makes a lot of sense. Still, it isn't uncommon (is it?) to have a binary with load-time dependencies on shared objects it expects to find (already compiled) on your system (in /lib or /usr/lib), even when you compile the project itself from source. Running ldd on an executable might show it depends on things like libc.so, libtinfo.so, libdl.so, libpthread.so etc. Would there not be linking problems if the version of your compiler was incompatible?
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