reflection.html

<cxx-clause id="reflection">
  <h1>Reflection library</h1>

  <cxx-section id="reflection.src_loc">
    <h1>Class <code>source_location</code></h1>

    <cxx-section id="reflection.src_loc.synop">
      <h1>Header <code>&lt;experimental/source_location></code> synopsis</h1>

<pre><code>namespace std {
namespace experimental {
inline namespace fundamentals_v2 {

  struct source_location {
    <cxx-ref insynopsis to="reflection.src_loc.creation"></cxx-ref>
    static constexpr source_location current() noexcept;

    constexpr source_location() noexcept;

    <cxx-ref insynopsis to="reflection.src_loc.fields"></cxx-ref>
    constexpr uint_least32_t line() const noexcept;
    constexpr uint_least32_t column() const noexcept;
    constexpr const char* file_name() const noexcept;
    constexpr const char* function_name() const noexcept;
  };

} // namespace fundamentals_v2
} // namespace experimental
} // namespace std</code></pre>

      <p>
        <cxx-note>The intent of <code>source_location</code> is to have a small size and efficient copying.</cxx-note>
      </p>
    </cxx-section>

    <cxx-section id="reflection.src_loc.creation">
      <h1><code>source_location</code> creation</h1>

      <cxx-function>
        <cxx-signature>static constexpr source_location current() noexcept;</cxx-signature>

        <cxx-returns>
          When invoked by a function call (<cxx-ref in="cxx" to="expr.call"></cxx-ref>)
          whose <cxx-grammarterm>postfix-expression</cxx-grammarterm> is
          a (possibly parenthesized) <cxx-grammarterm>id-expression</cxx-grammarterm> naming <code>current</code>,
          returns a <code>source_location</code> with an implementation-defined value.
          The value should be affected by <code>#line</code>
          (<cxx-ref in="cxx" to="cpp.line"></cxx-ref>) in the same manner as for <code>__LINE__</code> and <code>__FILE__</code>.
          If invoked in some other way, the value returned is unspecified.
        </cxx-returns>
        <cxx-remarks>
          When a <cxx-grammarterm>brace-or-equal-initializer</cxx-grammarterm> is used to initialize a non-static data member,
          any calls to <code>current</code> should correspond to the location of
          the constructor or aggregate initialization that initializes the member.
        </cxx-remarks>
        <p>
          <cxx-note>When used as a default argument (<cxx-ref in="cxx" to="dcl.fct.default"></cxx-ref>),
            the value of the <code>source_location</code> will be the location of the call to <code>current</code> at the call site.</cxx-note>
        </p>
        <cxx-example>
          <pre><code>struct s {
  source_location member = source_location::current();
  int other_member;
  s(source_location loc = source_location::current())
    : member(loc) // <i>values of</i> member <i>will be from call-site</i>
  {}
  s(int blather) : // <i>values of</i> member <i>should be hereabouts</i>
    other_member(blather) {}
  s(double) // <i>values of</i> member <i>should be hereabouts</i>
  {}
};

void f(source_location a = source_location::current()) {
  source_location b = source_location::current(); // <i>values in</i> b <i>represent this line</i>
}

void g() {
  f(); // f<i>’s first argument corresponds to this line of code</i>

  source_location c = source_location::current();
  f(c); // f<i>’s first argument gets the same values as </i>c<i>, above</i>
}</code></pre>
        </cxx-example>
      </cxx-function>

      <cxx-function>
        <cxx-signature>constexpr source_location() noexcept;</cxx-signature>

        <cxx-effects>Constructs an object of class <code>source_location</code>.</cxx-effects>
        <cxx-remarks>The values are implementation-defined.</cxx-remarks>
      </cxx-function>
    </cxx-section>

    <cxx-section id="reflection.src_loc.fields">
      <h1><code>source_location</code> field access</h1>

      <cxx-function>
        <cxx-signature>constexpr uint_least32_t line() const noexcept;</cxx-signature>

        <cxx-returns>The presumed line number (<cxx-ref in="cxx" to="cpp.predefined"></cxx-ref>) represented by this object.</cxx-returns>
      </cxx-function>

      <cxx-function>
        <cxx-signature>constexpr uint_least32_t column() const noexcept;</cxx-signature>

        <cxx-returns>
          An implementation-defined value representing
          some offset from the start of the line represented by this object.
        </cxx-returns>
      </cxx-function>

      <cxx-function>
        <cxx-signature>constexpr const char* file_name() const noexcept;</cxx-signature>

        <cxx-returns>
          The presumed name of the current source file (<cxx-ref in="cxx" to="cpp.predefined"></cxx-ref>)
          represented by this object as an NTBS.
        </cxx-returns>
      </cxx-function>

      <cxx-function>
        <cxx-signature>constexpr const char* function_name() const noexcept;</cxx-signature>

        <cxx-returns>
          If this object represents a position in the body of a function,
          returns an implementation-defined NTBS that should correspond to the function name.
          Otherwise, returns an empty string.
        </cxx-returns>
      </cxx-function>
    </cxx-section>
  </cxx-section>
</cxx-clause>