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<title>Service requirements</title>
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<div class="titlepage"><div><div><h3 class="title">
<a name="boost_asio.reference.Service"></a><a class="link" href="Service.html" title="Service requirements">Service requirements</a>
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<p>
A class is a <span class="emphasis"><em>service</em></span> if it is publicly and unambiguously
derived from <code class="computeroutput">execution_context::service</code>, or if it is publicly
and unambiguously derived from another service. For a service <code class="computeroutput">S</code>,
<code class="computeroutput">S::key_type</code> shall be valid and denote a type (C++Std [temp.deduct]),
<code class="computeroutput">is_base_of_v<typename S::key_type, S></code> shall be <code class="computeroutput">true</code>,
and <code class="computeroutput">S</code> shall satisfy the <code class="computeroutput">Destructible</code> requirements
(C++Std [destructible]).
</p>
<p>
The first parameter of all service constructors shall be an lvalue reference
to <code class="computeroutput">execution_context</code>. This parameter denotes the <code class="computeroutput">execution_context</code>
object that represents a set of services, of which the service object will
be a member. [<span class="emphasis"><em>Note:</em></span> These constructors may be called
by the <code class="computeroutput">make_service</code> function. —<span class="emphasis"><em>end note</em></span>]
</p>
<p>
A service shall provide an explicit constructor with a single parameter of
lvalue reference to <code class="computeroutput">execution_context</code>. [<span class="emphasis"><em>Note:</em></span>
This constructor may be called by the <code class="computeroutput">use_service</code> function.
—<span class="emphasis"><em>end note</em></span>]
</p>
<pre class="programlisting">class my_service : public execution_context::service
{
public:
typedef my_service key_type;
explicit my_service(execution_context& ctx);
my_service(execution_context& ctx, int some_value);
private:
virtual void shutdown() noexcept override;
...
};
</pre>
<p>
A service's <code class="computeroutput">shutdown</code> member function shall destroy all copies
of user-defined function objects that are held by the service.
</p>
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<td align="right"><div class="copyright-footer">Copyright © 2003-2018 Christopher M. Kohlhoff<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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