Am 07.01.25 um 16:16 schrieb Rainer Deyke via Boost:
On 06.01.25 19:43, Ivan Matek via Boost wrote:
boost::implies(student.graduaded(), student.num_active_courses() == 0) reads much much nicer than !student.graduaded() || student.num_active_courses() == 0
The problem here is that your example is closer to the English usage of the word "implies" than to the usage in boolean logic that we are talking about. "A implies B" in English usually means that there is a logical connection such that B is necessarily true if A is true. For example, a student who has graduated necessarily has no active courses.
"A => B" merely means that either A is false or B is true. For example, "I am the president of the United States => there is world peace" is trivially true because I am not the president of the United States, even though if I would almost certainly be unable to achieve world peace even if I were the president of the United States. The C++ expression "!A || B" is actually closer to the correct English than "A => B" for expressing this condition. Isn't that is exactly what was written above? I.e. `A => B` == `boost::implies(A, B)` == `!A || B`
Or with the example: if( boost::implies(student.graduaded(), student.num_active_courses() == 0) ) /*...*/;` In plain English: "If a graduated student implies he has no active courses" So I don't see how "!A || B" is closer to anything than "A => B" if they are the same thing. What am I missing here? Or did you mistype anything? Aside from that I don't actually see how that could be useful outside of asserts. I.e. `assert ( implies(this, that) )` makes sense and is readable. But `if implies(this, that)` not so much. Because it sounds much more general than it is it might be rather confusing. With your example `if( i_am_president() "implies" is_world_peace() )` is likely true right now, but if I became president at some point someone trusting this statement would likely be disappointed. Not that such things ever stopped any politician ;-) It still boils down to the English language which doesn't match the logical interpretation which is likely what you intended to say because also when reading the code `student.graduaded()` might not magically ensure `num_active_courses() == 0` although it reads (in English terms) that way. TLDR: I wouldn't want such a function or even operator as I don't see any reasonable uses outside of assertions.