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<html><head><meta content="text/html; charset=ISO-8859-1" http-equiv="Content-Type"><title>7. Practical considerations</title><meta name="generator" content="DocBook XSL Stylesheets V1.48"><link rel="home" href="index.html" title="
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C++ BOOST
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The Boost Lambda Library"><link rel="up" href="index.html" title="
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C++ BOOST
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The Boost Lambda Library"><link rel="previous" href="ar01s06.html" title="6. Extending return type deduction system"><link rel="next" href="ar01s08.html" title="8. Relation to other Boost libraries"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">7. Practical considerations</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ar01s06.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="ar01s08.html">Next</a></td></tr></table><hr></div><div class="section"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="id2807377"></a>7. Practical considerations</h2></div></div><div class="section"><div class="titlepage"><div><h3 class="title"><a name="id2807383"></a>7.1. Performance</h3></div></div><p>In theory, all overhead of using STL algorithms and lambda functors compared to hand written loops can be optimized away, just as the overhead from standard STL function objects and binders can.
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Depending on the compiler, this can also be true in practice.
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</p><p>We have only performed limited performance testing described in [<a href="bi01.html#cit:jarvi:00" title="[Jär00]">Jär00</a>], and
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our tests suggest that the BLL does not introduce a loss of performance compared to STL function objects.
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Hence, with a reasonable optimizing compiler, one should expect the performance characteristics be comparable to using classic STL.
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Moreover, with a great optimizing compiler there may be no performance penalty at all.
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Note however, that evaluating a lambda functor consist of a sequence of calls to small functions that are declared inline.
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If the compiler fails to actually expand these functions inline, the performance, compared to hand written loops, can suffer.
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</p></div><div class="section"><div class="titlepage"><div><h3 class="title"><a name="id2807426"></a>7.2. About compiling</h3></div></div><p>The BLL uses templates rather heavily, performing numerous recursive instantiations of the same templates.
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This has (at least) three implications:
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<div class="itemizedlist"><ul type="disc"><li><p>
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While it is possible to write incredibly complex lambda expressions, it probably isn't a good idea.
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Compiling such expressions may end up requiring a lot of memory
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at compile time, and being slow to compile.
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</p></li><li><p>
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The types of lambda functors that result from even the simplest lambda expressions are cryptic.
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Usually the programmer doesn't need to deal with the lambda functor the types at all, but in the case of an error in a lambda expression, the compiler usually outputs the types of the lambda functors involved.
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This can make the error messages very long and difficult to interpret, particularly if the compiler outputs the whole chain of template instantiations.
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</p></li><li><p>
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The C++ Standard suggests a template nesting level of 17 to help detect infinite recursion.
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Complex lambda templates can easily exceed this limit.
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Most compilers allow a greater number of nested templates, but commonly require the limit explicitly increased with a command line argument.
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</p></li></ul></div></p></div><div class="section"><div class="titlepage"><div><h3 class="title"><a name="id2807495"></a>7.3. Portability</h3></div></div><p>
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The BLL works with the following compilers, that is, the compilers are capable of compiling the test cases that are included with the BLL:
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<div class="itemizedlist"><ul type="disc"><li>GCC 3.0.2
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</li><li>KCC 4.0f with EDG 2.43.1
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</li><li>GCC 2.96 (fails with one test case, the <tt>exception_test.cpp</tt> results in an internal compiler error.
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)
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</li></ul></div>
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</p><div class="section"><div class="titlepage"><div><h4 class="title"><a name="id2807535"></a>7.3.1. Test coverage</h4></div></div><p>The following list describes the test files included and the features that each file covers:
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<div class="itemizedlist"><ul type="disc"><li><p>
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<tt>bind_tests_simple.cpp</tt> : Bind expressions of different arities and types of target functions: function pointers, function objects and member functions.
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Function composition with bind expressions.</p></li><li><p><tt>bind_tests_simple_function_references.cpp</tt> :
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Repeats all tests from <tt>bind_tests_simple.cpp</tt> where the target function is a function pointer, but uses function references instead.
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</p></li><li><p><tt>bind_tests_advanced.cpp</tt> : Contains tests for nested bind expressions, <tt>unlambda</tt>, <tt>protect</tt>, <tt>const_parameters</tt> and <tt>break_const</tt>.
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Tests passing lambda functors as actual arguments to other lambda functors, currying, and using the <tt>sig</tt> template to specify the return type of a function object.
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</p></li><li><p>
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<tt>operator_tests_simple.cpp</tt> :
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Tests using all operators that are overloaded for lambda expressions, that is, unary and binary arithmetic,
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bitwise,
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comparison,
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logical,
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increment and decrement,
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compound,
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assignment,
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subscrict,
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address of,
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dereference, and comma operators.
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The streaming nature of shift operators is tested, as well as pointer arithmetic with plus and minus operators.
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</p></li><li><p><tt>member_pointer_test.cpp</tt> : The pointer to member operator is complex enough to warrant a separate test file.
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</p></li><li><p>
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<tt>control_structures.cpp</tt> :
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Tests for the looping and if constructs.
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</p></li><li><p>
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<tt>switch_construct.cpp</tt> :
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Includes tests for all supported arities of the switch statement, both with and without the default case.
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</p></li><li><p>
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<tt>exception_test.cpp</tt> :
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Includes tests for throwing exceptions and for try/catch constructs with varying number of catch blocks.
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</p></li><li><p>
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<tt>constructor_tests.cpp</tt> :
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Contains tests for <tt>constructor</tt>, <tt>destructor</tt>, <tt>new_ptr</tt>, <tt>delete_ptr</tt>, <tt>new_array</tt> and <tt>delete_array</tt>.
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</p></li><li><p>
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<tt>cast_test.cpp</tt> : Tests for the four cast expressions, as well as <tt>typeid</tt> and <tt>sizeof</tt>.
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</p></li><li><p>
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<tt>extending_return_type_traits.cpp</tt> : Tests extending the return type deduction system for user defined types.
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Contains several user defined operators and the corresponding specializations for the return type deduction templates.
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</p></li><li><p>
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<tt>is_instance_of_test.cpp</tt> : Includes tests for an internally used traits template, which can detect whether a given type is an instance of a certain template or not.
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</p></li><li><p>
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<tt>bll_and_function.cpp</tt> :
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Contains tests for using <tt>boost::function</tt> together with lambda functors.
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</p></li></ul></div>
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</p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ar01s06.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="index.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ar01s08.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">6. Extending return type deduction system </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 8. Relation to other Boost libraries</td></tr></table></div></body></html>
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