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describe SmallSetVector

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llvm-svn: 33847
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Chris Lattner 2007-02-04 00:00:26 +00:00
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docs/ProgrammersManual.html
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@ -1016,8 +1016,9 @@ std::set is almost never a good choice.</p>
</div>
<div class="doc_text">
<p>LLVM's SetVector&lt;Type&gt; is actually a combination of a set along with
a <a href="#ds_sequential">Sequential Container</a>. The important property
<p>LLVM's SetVector&lt;Type&gt; is an adapter class that combines your choice of
a set-like container along with a <a href="#ds_sequential">Sequential
Container</a>. The important property
that this provides is efficient insertion with uniquing (duplicate elements are
ignored) with iteration support. It implements this by inserting elements into
both a set-like container and the sequential container, using the set-like
@ -1028,7 +1029,7 @@ container for uniquing and the sequential container for iteration.
iteration is guaranteed to match the order of insertion into the SetVector.
This property is really important for things like sets of pointers. Because
pointer values are non-deterministic (e.g. vary across runs of the program on
different machines), iterating over the pointers in a std::set or other set will
different machines), iterating over the pointers in the set will
not be in a well-defined order.</p>
<p>
@ -1036,9 +1037,17 @@ The drawback of SetVector is that it requires twice as much space as a normal
set and has the sum of constant factors from the set-like container and the
sequential container that it uses. Use it *only* if you need to iterate over
the elements in a deterministic order. SetVector is also expensive to delete
elements out of (linear time).
elements out of (linear time), unless you use it's "pop_back" method, which is
faster.
</p>
<p>SetVector is an adapter class that defaults to using std::vector and std::set
for the underlying containers, so it is quite expensive. However,
<tt>"llvm/ADT/SetVector.h"</tt> also provides a SmallSetVector class, which
defaults to using a SmallVector and SmallSet of a specified size. If you use
this, and if your sets are dynamically smaller than N, you will save a lot of
heap traffic.</p>
</div>
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