<p>I'll leave this pull request open for a week, for the sake of discussion, since it's a major change</p>
<p>In the past, the great idea was come upon that a <code>ToString()</code> method should be implemented in every class, then some glue logic could allow <code>operator<<()</code> for any arbitrary mlpack object. This was done with template metaprogramming (see <code>sfinae_utility.hpp</code> by Trironk, it is quite cool) and worked fine.</p>
<p>However, as time has gone on, it's unclear to me whether or not this feature is actually useful, and personally I am of the opinion that it should be removed, so I made a few commits removing all the <code>ToString()</code> functions and related functionality and made this pull request. Here are my arguments for why it isn't very useful:</p>
<ul>
<li><p>It's not always clear how much should be printed in a <code>ToString()</code> call. Should we print all of a binary space tree? Only the first few levels? How much information does the user want? In many cases, the amount of information that <em>could</em> be printed is huge, so when a user sends an object to an ostream, they get reams and reams of output.</p></li>
<li><p>It's extra overhead for new contributors and also for maintenance, if their classes also have to have a <code>ToString()</code> method. And usually when these are written, it seems like simple copypasta and not much thought is given into precisely what to display (see the previous point).</p></li>
<li><p>It's not actually all that useful for debugging; often when debugging, I find myself ignoring the <code>ToString()</code> function and instead only printing the member of the object that I am interested in.</p></li>
</ul>
<p>So, those are the primary reasons I think that we should remove---or at least rethink---the <code>ToString()</code> functionality. Like I said, I'll leave this open for a week for discussion, then merge in the change. So if you disagree with anything I've written here, or you find the <code>ToString()</code> functions particularly useful, feel free to comment! My perspective is not the only perspective. :)</p>
<hr>
<h4>You can view, comment on, or merge this pull request online at:</h4>
<p> <a href='https://github.com/mlpack/mlpack/pull/487'>https://github.com/mlpack/mlpack/pull/487</a></p>
<h4>Commit Summary</h4>
<ul>
<li>Remove ToString() from everything.</li>
<li>Update HISTORY.md.</li>
<li>Remove special handling for ToString().</li>
</ul>
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<strong>M</strong>
<a href="https://github.com/mlpack/mlpack/pull/487/files#diff-104">src/mlpack/methods/sparse_coding/sparse_coding_impl.hpp</a>
(13)
</li>
<li>
<strong>M</strong>
<a href="https://github.com/mlpack/mlpack/pull/487/files#diff-105">src/mlpack/tests/CMakeLists.txt</a>
(1)
</li>
<li>
<strong>D</strong>
<a href="https://github.com/mlpack/mlpack/pull/487/files#diff-106">src/mlpack/tests/to_string_test.cpp</a>
(533)
</li>
</ul>
<h4>Patch Links:</h4>
<ul>
<li><a href='https://github.com/mlpack/mlpack/pull/487.patch'>https://github.com/mlpack/mlpack/pull/487.patch</a></li>
<li><a href='https://github.com/mlpack/mlpack/pull/487.diff'>https://github.com/mlpack/mlpack/pull/487.diff</a></li>
</ul>
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