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| <div class="section" id="exercises"> |
| <h1><a class="toc-backref" href="./tutorial-metafunctions.html#id60" name="exercises">Exercises</a></h1> |
| <dl> |
| <dt>1-0.</dt> |
| <dd>Use <tt class="literal"><span class="pre">BOOST_STATIC_ASSERT</span></tt> to add error checking to the <tt class="literal"><span class="pre">binary</span></tt> |
| template presented in section <a class="reference" href="./resources.html">1</a>.4.1 so |
| that <tt class="literal"><span class="pre">binary<N>::value</span></tt> causes a compilation error if <tt class="literal"><span class="pre">N</span></tt> |
| contains digits other than <tt class="literal"><span class="pre">0</span></tt> or <tt class="literal"><span class="pre">1</span></tt>.</dd> |
| <dt>1-1.</dt> |
| <dd>Turn <tt class="literal"><span class="pre">vector_c<int,1,2,3></span></tt> into a type sequence with elements |
| (2,3,4) using <tt class="literal"><span class="pre">transform</span></tt>.</dd> |
| <dt>1-2.</dt> |
| <dd>Turn <tt class="literal"><span class="pre">vector_c<int,1,2,3></span></tt> into a type sequence with elements |
| (1,4,9) using <tt class="literal"><span class="pre">transform</span></tt>.</dd> |
| <dt>1-3.</dt> |
| <dd>Turn <tt class="literal"><span class="pre">T</span></tt> into <tt class="literal"><span class="pre">T****</span></tt> by using <tt class="literal"><span class="pre">twice</span></tt> twice.</dd> |
| <dt>1-4.</dt> |
| <dd>Turn <tt class="literal"><span class="pre">T</span></tt> into <tt class="literal"><span class="pre">T****</span></tt> using <tt class="literal"><span class="pre">twice</span></tt> on itself.</dd> |
| <dt>1-5.</dt> |
| <dd><p class="first">There's still a problem with the dimensional analysis code in |
| section 1.1. |
| Hint: What happens when you do:</p> |
| <pre class="literal-block"> |
| f = f + m * a; |
| </pre> |
| <p>Repair this example using techniques shown in this |
| chapter.</p> |
| <!-- @ example.wrap('''void will_fail%s |
| { quantity<float,force> f(m*a); |
| ''' % ma_function_args, '}') |
| stack[:0] = dimensional_analysis # stick support code in |
| compile('all', expect_error = True) --> |
| </dd> |
| <dt>1-6.</dt> |
| <dd>Build a lambda expression that has functionality equivalent to |
| <tt class="literal"><span class="pre">twice</span></tt>. Hint: <tt class="literal"><span class="pre">mpl::apply</span></tt> is a metafunction!</dd> |
| <dt>1-7*.</dt> |
| <dd><p class="first">What do you think would be the semantics of the following |
| constructs:</p> |
| <pre class="literal-block"> |
| typedef mpl::lambda<mpl::lambda<_1> >::type t1; |
| typedef mpl::apply<_1,mpl::plus<_1,_2> >::type t2; |
| typedef mpl::apply<_1,std::vector<int> >::type t3; |
| typedef mpl::apply<_1,std::vector<_1> >::type t4; |
| typedef mpl::apply<mpl::lambda<_1>,std::vector<int> >::type t5; |
| typedef mpl::apply<mpl::lambda<_1>,std::vector<_1> >::type t6; |
| typedef mpl::apply<mpl::lambda<_1>,mpl::plus<_1,_2> >::type t7; |
| typedef mpl::apply<_1,mpl::lambda< mpl::plus<_1,_2> > >::type t8; |
| </pre> |
| <!-- @example.prepend('#include <vector>') |
| compile() --> |
| <p class="last">Show the steps used to |
| arrive at your answers and write tests verifying your assumptions. |
| Did the library behavior match your reasoning? If not, analyze the |
| failed tests to discover the actual expression semantics. |
| Explain why your assumptions were different, what |
| behavior you find more coherent, and why.</p> |
| </dd> |
| <dt>1-8*.</dt> |
| <dd>Our dimensional analysis framework dealt with dimensions, but it |
| entirely ignored the issue of <em>units</em>. A length can be |
| represented in inches, feet, or meters. A force can be |
| represented in newtons or in kg m/sec<sup>2</sup>. Add the |
| ability to specify units and test your code. Try to make your |
| interface as syntactically friendly as possible for the user.</dd> |
| </dl> |
| <!-- Along with Alan Turing, Church was one of the founders of computer |
| science. --> |
| <!-- yes, this is easier to read, but the real beauty of ``apply`` is that |
| it not only works on metafunction classes, but on metafunctions passed |
| with placeholder arguments. --> |
| <!-- Naturally, MPL defines a series of these numbered placeholder |
| types, so that we can handle metafunctions with more arguments. --> |
| <!-- : in order to pass a template in the ``BinaryOperation`` position, |
| ``transform`` would have to be declared:: |
| |
| template < |
| class Sequence1, class Sequence2 |
| , template <class,class> class BinaryOperation |
| > |
| struct transform; // returning a sequence --> |
| <!-- "Programming with types" --> |
| <!-- Once again, a nested ``value`` member is optional for |
| metafunctions, and required for integral type wrappers. --> |
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