<html>
    <head>
      <base href="https://llvm.org/bugs/" />
    </head>
    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW "
   title="NEW --- - improve error when binding to wrong placeholder"
   href="https://llvm.org/bugs/show_bug.cgi?id=23047">23047</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>improve error when binding to wrong placeholder
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>clang
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>trunk
          </td>
        </tr>

        <tr>
          <th>Hardware</th>
          <td>PC
          </td>
        </tr>

        <tr>
          <th>OS</th>
          <td>All
          </td>
        </tr>

        <tr>
          <th>Status</th>
          <td>NEW
          </td>
        </tr>

        <tr>
          <th>Severity</th>
          <td>normal
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>P
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>C++
          </td>
        </tr>

        <tr>
          <th>Assignee</th>
          <td>unassignedclangbugs@nondot.org
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>nlewycky@google.com
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>dgregor@apple.com, llvmbugs@cs.uiuc.edu
          </td>
        </tr>

        <tr>
          <th>Classification</th>
          <td>Unclassified
          </td>
        </tr></table>
      <p>
        <div>
        <pre>We should product a nice error message for this mistake:

#include <functional>
#include <string>

void Print(const std::string& a, const std::string& b, const std::string& c);

void test() {
  std::function<void(const std::string&)> func =
      std::bind(&Print, "aaa", std::placeholders::_2, "ccc");
  func("garbage");
}

I'm not going to paste the template spew we get with libstdc++ today. I don't
know what we get with libc++.

What I want is an error message along the lines of "tried to use _2 placeholder
for a 1 argument function type". I'm not sure whether this should be strictly
in the compiler, or whether we can have collusion with the library
implementation.</pre>
        </div>
      </p>
      <hr>
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      <ul>
          <li>You are on the CC list for the bug.</li>
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