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How do you handle a constructor that fails?
The best way to signal constructor failure is therefore to throw an exception. If you don’t have the option of using exceptions, the “least bad” work-around is to put the object into a “zombie” state by setting an internal status bit so the object acts sort of like it’s dead even though it is technically still alive.
What happens when a constructor fails?
A constructor cannot possibly recover and do something sensible after one of its base or member subobjects’ constructors throws. It cannot even put its own object into a “construction failed” state.
Can constructor fail?
The ‘real’ constructor is still private and cannot fail. This might sound an overkill, but lambdas are optimized wonderfully by compilers. You might even spare the if of the optional this way.
Is it good to throw exception from constructor?
Throwing exceptions in a constructor is not bad practice. In fact, it is the only reasonable way for a constructor to indicate that there is a problem; e.g. that the parameters are invalid.
Can constructor fail C++?
The ‘real’ constructor is still private and cannot fail. This might sound an overkill, but lambdas are optimized wonderfully by compilers.
How to handle failure in constructor in C + +?
A (member or global) function that works only on valid objects works on T. One that surely returns valid works on T. One that might return an invalid object return optional . One that might invalidate an object take non-const optional & or optional *.
When to throw an exception in a constructor?
A constructor may well open a file (not necessarily a bad idea) and may throw if the file-open fails, or if the input file does not contain compatible data. It is reasonable behaviour for a constructor to throw an exception, however you will then be limited as to its use.
Is it wrong to open a file in the constructor?
Some comments here say it’s wrong to open a file in the constructor. I’ll point out that ifstream is part of the C++ standard it has the following constructor: A constructor may well open a file (not necessarily a bad idea) and may throw if the file-open fails, or if the input file does not contain compatible data.
How to replace a constructor in functional style?
Functional style: The good news is, (non-named) constructors are never virtual. Therefore, you can replace them with a static template member function that, apart from the constructor parameters, takes two (or more) lambdas: one if it was successful, one if it failed.