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    <p>There are multiple things which result in multiple instantiations not being too harmful to the exacutable size:</p> <ol> <li>Many templates are just passing things through to another layer. Although there may be quite a bit of code it mostly disappears when the code is instantiated and inlined. Note inlining [and doing some optimizations] can easily result in bigger code, though. Note that inlining <em>small</em> functions often results in <em>smaller</em> (and faster) code (basically because the otherwise necessary calling sequence often requires more instructions than what is inlined and the optimizer gets a better chance to further reduce the code by a more holistic view of what's going on).</li> <li>Where template code isn't inlined, duplicate instantiations in different translation units need to be merged into just one instantiation. I'm not a linker expert but my understanding is that, e.g., ELF uses different sections and the linker can choose to include only those sections which are actually used.</li> <li>In bigger executables you'll need some vocabulary types and instantiations which used in many places and effectively shared. Doing everything using a custom type would be bad idea and type erasure is certainly an important tool to avoid too many types.</li> </ol> <p>That said, where possible it does pay off to preinstantiate templates, especially if there are only a small number of instantations which are generally used. A great example is the IOStreams library which is unlikely to be used with more than 4 types (typically it is used with just one): moving the template definitions and their instantiations into separate translation units may not reduce the executable size but will certainly reduce the compile time! Starting with C++11 it is possible to declare template instantiations as <code>extern</code> which allows the definitions to be visible without getting implicitly instantiated on specializations which are known to be instantiated elsewhere.</p>
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    1. POHow do C++ compilers optimize template code?
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    1. USDietmar Kühl
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    1. COalso I think that the OP is starting from the ( wrong ) idea that templates = functions, but this is clearly wrong, templates in C++ are an example of metaprogramming, it's a technology that generates software inside your software, a function is a more imperative and less abstract concept. there are also different mechanisms involved, for example too many times a partial specialization for a template it's called "overloading", and this is something that could lead someone to think that this works just as function overloading at runtime.
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