<p> Here <code><i>MAX_ARGS</i></code> is an implementation-defined constant that defines the maximum number of function arguments supported by Boost.Function and will be at least 10. The <code><i>MAX_ARGS</i></code> constant referred to in this document need not have any direct representation in the library.
<li><aname="compatible"></a>A function object <code>f</code> is <em>compatible</em> if for the given set of argument types <code>Arg1</code>, <code>Arg2</code>, ..., <code>Arg<em>N</em></code> and a return type <code>ResultType</code>, the appropriate following function is well-formed:
<p> A special provision is made for pointers to member functions. Though they are not function objects, Boost.Function will adapt them internally to function objects. This requires that a pointer to member function of the form <code>R (X::*mf)(Arg1, Arg2, ..., Arg<em>N</em>) <em>cv-quals</em></code> be adapted to a function object with the following function call operator overloads:
<p> Class <code>function_base</code> is the common base class for all Boost.Function objects. Objects of type <code>function_base</code> may not be created directly.
<li><b>Returns</b>: <code>safe_bool</code> equivalent of <code>!<ahref="#empty">empty</a>()</code></li>
<li><b>Throws</b>: will not throw.</li>
<li><b>Notes</b>: The <code>safe_bool</code> type can be used in contexts where a <b>bool</b> is expected (e.g., an <b>if</b> condition); however, implicit conversions (e.g., to <b>int</b>) that can occur with <b>bool</b> are not allowed, eliminating some sources of user error.
<p> Class template <code>function<i>N</i></code> is actually a family of related classes <code>function0</code>, <code>function1</code>, etc., up to some implementation-defined maximum. In this context, <code><i>N</i></code> refers to the number of parameters and <code>f</code> refers to the implicit object parameter.
<li><b>Postconditions</b>: <code>f</code> contains a copy of the <code>g</code>'s target, if it has one, or is empty if <code>g.<ahref="#empty">empty</a>()</code>. The mixin for the <code>f</code> is copy-constructed from the mixin of <code>g</code>.</li>
<li><b>Effects</b>: Constructs the <code>Mixin</code> subobject from the given mixin.</li>
<li><b>Postconditions</b>: <code>f</code> targets a copy of <code>g</code> if <code>g</code> is nonempty, or <code>f.<ahref="#empty">empty</a>()</code> if <code>g</code> is empty.</li>
<li><b>Rationale</b>: <code>g</code> is a reference-to-<code><b>const</b></code> because it is a portable, efficient, and concise way to accept any function object or function pointer. In the case of a function pointer, the type of <code>g</code> is reference-to-<code><b>const</b></code> pointer-to-function.</li>
<li><b>Requires</b>: <code>g.get()</code> is a <ahref="#compatible">compatible</a> function object.</li>
<li><b>Effects</b>: Constructs the <code>Mixin</code> subobject from the given mixin.</li>
<li><b>Postconditions</b>: <code>this</code> object targets <code>g</code> (<em>not</em> a copy of <code>g.get()</code>) if <code>g.get()</code> is nonempty, or <code>this->empty()</code> if <code>g.get()</code> is empty.</li>
<li><b>Postconditions</b>: <code>f</code> targets a copy of <code>g</code>'s target, if it has one, or is empty if <code>g.<ahref="#empty">empty</a>()</code>. The mixin for <code>f</code> is assigned the value of the mixin for <code>g</code>.</li>
<li><b>Postconditions</b>: <code>f</code> targets a copy of <code>g</code> if <code>g</code> is nonempty, or <code>f.<ahref="#empty">empty</a>()</code> if <code>g</code> is empty.</li>
<li><b>Rationale</b>: <code>g</code> is a reference-to-<code><b>const</b></code> because it is a portable, efficient, and concise way to accept any function object or function pointer. In the case of a function pointer, the type of <code>g</code> is reference-to-<code><b>const</b></code> pointer-to-function.</li>
<li><b>Requires</b>: <code>g.get()</code> is a <ahref="#compatible">compatible</a> function object.</li>
<li><b>Postconditions</b>: <code>f</code> targets <code>g.get()</code> (not a copy of <code>g.get()</code>) if <code>g.get()</code> is nonempty, or <code>f.<ahref="#empty">empty</a>()</code> if <code>g.get()</code> is empty.</li>
<li><b>Returns</b>: <code>*this</code>.</li>
<li><b>Throws</b>: will throw only if the destruction or deallocation of the target of <code>this</code> throws.</li>
<p> Class template <code>function</code> is a thin wrapper around the numbered class templates <code>function0</code>, <code>function1</code>, etc. It accepts up to <i>MAX_ARGS</i> arguments, but when passed <i>N</i> arguments it will derive from <code>function<i>N</i></code> specialized with the arguments it receives.
<p> The semantics of all operations in class template <code>function</code> are equivalent to that of the underlying <code>function<i>N</i></code> object, although additional member functions are required to allow proper copy construction and copy assignment of <code>function</code> objects.
