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128 lines
3.3 KiB
C++
128 lines
3.3 KiB
C++
// Copyright (c) 2018-2019 Emil Dotchevski and Reverge Studios, Inc.
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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// This program demonstrates the use of leaf::accumulate to capture the path an error takes
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// as is bubbles up the call stack. The error path-capturing code only runs if:
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// - An error occurs, and
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// - A handler that takes e_error_trace argument is present.
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// Otherwise none of the error trace machinery will be invoked by LEAF.
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// This example is similar to error_log, except the path the error takes is captured and
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// recorded in a std::deque, rather than just printed in-place.
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#include <boost/leaf/preload.hpp>
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#include <boost/leaf/handle_error.hpp>
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#include <boost/leaf/result.hpp>
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#include <iostream>
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#include <deque>
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#include <cstdlib>
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#define ENABLE_ERROR_TRACE 1
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namespace leaf = boost::leaf;
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// The error trace is activated only if an error-handling scope provides a handler for e_error_trace.
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// This activation logic applies to any type passed to leaf::accumulate.
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struct e_error_trace
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{
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struct rec
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{
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char const * file;
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int line;
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friend std::ostream & operator<<( std::ostream & os, rec const & x )
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{
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return os << x.file << '(' << x.line << ')' << std::endl;
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}
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};
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std::deque<rec> value;
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friend std::ostream & operator<<( std::ostream & os, e_error_trace const & tr )
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{
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for( auto & i : tr.value )
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os << i;
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return os;
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}
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};
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// The ERROR_TRACE macro is designed for use in functions that detect or forward errors
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// up the call stack. If an error occurs, and if an error-handling scope provides a handler
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// for e_error_trace, the supplied lambda is executed as the error bubbles up.
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#define ERROR_TRACE auto _trace = leaf::accumulate( []( e_error_trace & tr ) { tr.value.emplace_front(e_error_trace::rec{__FILE__, __LINE__}); } )
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// Each function in the sequence below calls the previous function, and each function has
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// failure_percent chance of failing. If a failure occurs, the ERROR_TRACE macro will cause
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// the path the error takes to be captured in an e_error_trace.
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int const failure_percent = 25;
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leaf::result<void> f1()
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{
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ERROR_TRACE;
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if( (std::rand()%100) > failure_percent )
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return { };
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else
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return leaf::new_error();
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}
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leaf::result<void> f2()
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{
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ERROR_TRACE;
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if( (std::rand()%100) > failure_percent )
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return f1();
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else
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return leaf::new_error();
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}
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leaf::result<void> f3()
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{
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ERROR_TRACE;
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if( (std::rand()%100) > failure_percent )
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return f2();
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else
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return leaf::new_error();
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}
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leaf::result<void> f4()
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{
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ERROR_TRACE;
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if( (std::rand()%100) > failure_percent )
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return f3();
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else
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return leaf::new_error();
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}
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leaf::result<void> f5()
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{
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ERROR_TRACE;
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if( (std::rand()%100) > failure_percent )
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return f4();
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else
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return leaf::new_error();
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}
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int main()
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{
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for( int i=0; i!=10; ++i )
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leaf::try_handle_all(
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[&]() -> leaf::result<void>
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{
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std::cout << "Run # " << i << ": ";
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LEAF_CHECK(f5());
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std::cout << "Success!" << std::endl;
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return { };
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},
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#if ENABLE_ERROR_TRACE // This single #if enables or disables the capturing of the error trace.
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[]( e_error_trace const & tr )
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{
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std::cerr << "Error! Trace:" << std::endl << tr;
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},
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#endif
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[]
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{
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std::cerr << "Error!" << std::endl;
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} );
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return 0;
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}
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