You’ve got it in reverse: A cast from an object of a base class to a subclass will always fail, because the base class has only the properties of the the base class (not the subclass). Since, as you say, the subclass has all the properties of the base class (it “is-a” base-class object), then … Read more
When casting floats to integers, overflow causes undefined behavior. From the C99 spec, section 6.3.1.4 Real floating and integer: When a finite value of real floating type is converted to an integer type other than _Bool, the fractional part is discarded (i.e., the value is truncated toward zero). If the value of the integral part … Read more
RepositoryBase<EntityBase> is not a base class of MyEntityRepository. You’re looking for generic variance which exists in C# to a limited extent, but wouldn’t apply here. Suppose your RepositoryBase<T> class had a method like this: void Add(T entity) { … } Now consider: MyEntityRepository myEntityRepo = GetMyEntityRepo(); // whatever RepositoryBase<EntityBase> baseRepo = (RepositoryBase<EntityBase>)myEntityRepo; baseRepo.Add(new OtherEntity(…)); Now … Read more
Both Integer and Long are subclasses of Number, so I suspect you can use: long ipInt = ((Number) obj.get(“ipInt”)).longValue(); That should work whether the value returned by obj.get(“ipInt”) is an Integer reference or a Long reference. It has the downside that it will also silently continue if ipInt has been specified as a floating point … Read more
In general, when a mutable variable is captured in a lambda function closure, smart casts are not applicable to that variable, both inside the lambda and in the declaring scope after the lambda was created. It’s because the function may escape from its enclosing scope and may be executed later in a different context, possibly … Read more
If you only deal with integers, you can use str.isdigit(): Return true if all characters in the string are digits and there is at least one character, false otherwise. [row for row in listOfLists if row[x].isdigit()] Or if negative integers are possible (but should be allowed): row[x].lstrip(‘-‘).isdigit() And of course this all works only if … Read more
Class.cast is what you want. Well, you might consider not using reflection. Change the line: T result = (T)store.get(e); to: T result = exampleClass.cast(store.get(e));
A type cast is basically a conversion from one type to another. It can be implicit (i.e., done automatically by the compiler, perhaps losing info in the process) or explicit (i.e., specified by the developer in the code). The space occupied by the types is of secondary importance. More important is the applicability (and sometimes … Read more
as will never throw a InvalidCastException. Instead, it returns null if the cast fails (which would give you a NullReferenceException if obj in your example were not a string).
The main reason is that classic C casts make no distinction between what we call static_cast<>(), reinterpret_cast<>(), const_cast<>(), and dynamic_cast<>(). These four things are completely different. A static_cast<>() is usually safe. There is a valid conversion in the language, or an appropriate constructor that makes it possible. The only time it’s a bit risky is … Read more