c++/boost/gnc_numeric question

Geert Janssens geert.gnucash at kobaltwit.be
Sat Jan 14 06:54:42 EST 2017


The last few days I have payed some attention to our Travis-CI integration. Good news is we can 
now run our unit tests based on google test (thanks to John as well for some extra fixes).

The bad news is my csv-import work fails to build on travis while it builds just fine on my local 
system. The most recent build failure can be seen here:


This has been failing for a while, even before fixing the gtest stuff. My investigation seems to 
suggest the issues stems from using a different version of boost on my system (1.60.0) versus 
the one used on travis (1.54.0).

The failure is in this line:
    if ((m_deposit == boost::none) &&
        (m_withdrawal == boost::none))
with both m_deposit and m_withdrawal being of type
It appears boost 1.54.0 doesn't know how to run this comparison and the boost::optional 
revision history suggests this was addressed in version 1.56.0 [1].

Since our boost baseline is still 1.53.0, I'm looking for ways to handle this differently. 
gnc_numeric is a C struct. My csv-importer work however is all in c++, so why not use the 
underlying c++ code of gnc_numeric directly, right ?

So I am working my way through this and have some questions about this.

1. I assumed the C++ equivalent of gnc_numeric would be GncNumeric. However this appears 
to be wrong assumption. GncNumeric is only defined as an alias inside gnc-numeric.cpp and 
hence not exposed at all to the outside world. Is new c++ code not supposed to use 
GncNumeric ? Should GncRational be used directly instead ?

2. I continued with GncRational for now. However this seems to implement only fairly limited 
subset of the functions in gnc_numeric. For example there is gnc_numeric_mul and 
GncRational::mul. The former takes two extra parameters (one for denom preference and one to 
tell how to round). GncRational::mul on the other hand takes a denom object as second 
parameter which encapsulates all that information in addition to the two objects we're about to 
multiply. I'm not sure how I should use this. Should each consumer of the GncRational class 
each time build the denom object itself and then call the GncRational mutators ? That looks like 
a lot of code overhead. How about an overload for these mutators that takes the denom and 
round type directly as gnc_numeric_mul does ? Or is there another way to use this I didn't figure 
out yet ?

3. While studying the GncRational code I noted it has doesn't specify the pure constructor 
"GncRational()", instead leaving this up to the compiler to generate if necessary. That compiler 
default would create a GncRational with m_num = 0, m_denom = 0 and m_error = 
GNC_ERROR_OK. I would consider
m_num = 0, m_denom = 1 and m_error = GNC_ERROR_OK a better default value for 
GncRational. A particular reason not to implement that ?



[1] from http://www.boost.org/doc/libs/1_60_0/libs/optional/doc/html/boost_optional/
relnotes.html :
'Equality comparison with boost::none does not require that T be EqualityComparable,'

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