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POHow can I pass a lambda (c++11) into a templated function?
 

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  1. POHow can I pass a lambda (c++11) into a templated function?
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    <p>I'm playing around with lambda functions in gcc 4.6.2, and would like to implement a templated "map" function like this:</p> <pre><code>template&lt;typename A, typename B&gt; std::vector&lt;B&gt; map(const std::vector&lt;A&gt;&amp; orig, const std::function&lt;B(A)&gt; f) { std::vector&lt;B&gt; rv; rv.resize(orig.size()); std::transform(begin(orig), end(orig), begin(rv), f); return rv; } </code></pre> <p>This doesn't work, because the test code:</p> <pre><code>int main(int argc, char **argv) { std::vector&lt;int&gt; list; list.push_back(10); list.push_back(20); list.push_back(50); std::vector&lt;int&gt; transformed = map(list, [](int x) -&gt; int { return x + 1; }); std::for_each(begin(transformed), end(transformed), [](int x) { printf("-&gt; %d\n", x); }); return 0; } </code></pre> <p>gives this error:</p> <pre class="lang-none prettyprint-override"><code>test.cpp:49:80: error: no matching function for call to ‘map(std::vector&lt;int&gt;&amp;, main(int, char**)::&lt;lambda(int)&gt;)’ test.cpp:49:80: note: candidate is: test.cpp:6:49: note: template&lt;class A, class B&gt; std::vector&lt;B&gt; map(const std::vector&lt;A&gt;&amp;, std::function&lt;B(A)&gt;) </code></pre> <p>If I remove the templating, and use a vector directly, it compiles fine:</p> <pre><code>std::vector&lt;int&gt; map(const std::vector&lt;int&gt;&amp; orig, const std::function&lt;int(int)&gt; f) { std::vector&lt;int&gt; rv; rv.resize(orig.size()); std::transform(begin(orig), end(orig), begin(rv), f); return rv; } </code></pre> <p>so it must be a problem with the way I'm defining the template.</p> <p>Has anyone run into this before? I know lambdas are incredibly new.</p>
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    1. COYou do know that in the examples in your post, you define the function `map` while calling `map_`? Note the underscore in the call... :-)
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    2. COSorry about the typos -- I was pasting this from a file with a dozen different attempts, to see if I could get the compiler to give me a better clue about what it didn't like. Think I've fixed those now.
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