casting

问题 I am going through a book on C# and have come across something that I can't seem to look up, because I don't know what it is called, or trying to search for something by description. Could some explain to me what is going on, or the meaning behind the (type) that comes before a reference to an object as in (int)objectname.variablename ? It seems like casting to me. EDIT: Since most of you are going off 'My' reference to casting when I am only guessing, and needed more code, I am including the

问题 I have a generic interface, lets call it GenericInterface<T> . I need to pass the class object of that interface to a method that expects (specified through another type parameter) a specific instance of that type. Let's assume I want to call java.util.Collections.checkedList() : List<GenericInterface<Integer>> list = Collections.checkedList( new ArrayList<GenericInterface<Integer>>(), GenericInterface.class); This does not work because Class<GenericInterface> cannot be implicitly casted to

问题 I have a generic interface, lets call it GenericInterface<T> . I need to pass the class object of that interface to a method that expects (specified through another type parameter) a specific instance of that type. Let's assume I want to call java.util.Collections.checkedList() : List<GenericInterface<Integer>> list = Collections.checkedList( new ArrayList<GenericInterface<Integer>>(), GenericInterface.class); This does not work because Class<GenericInterface> cannot be implicitly casted to

问题 We have an asp.net MVC web application which uses the HttpRuntime.Cache object to keep some static lookup values. We want to be able to monitor what's being cached in real time to allow us to pinpoint some possible caching issues. Since this object isn't strongly typed when reading from it, we need to dynamically cast each entries to it's concrete type. Most of the cached items are of IEnumerable where T can be any classes we use in our project or new ones that could eventually be added as

问题 We have an asp.net MVC web application which uses the HttpRuntime.Cache object to keep some static lookup values. We want to be able to monitor what's being cached in real time to allow us to pinpoint some possible caching issues. Since this object isn't strongly typed when reading from it, we need to dynamically cast each entries to it's concrete type. Most of the cached items are of IEnumerable where T can be any classes we use in our project or new ones that could eventually be added as

问题 I would like to know the rules specified by the C++ language standard for situations like: long x = 200; short y = static_cast<short>(x); Is y guaranteed to be 200, or does the standard leave this up to the implementation to decide? How well do various compilers adhere to the standard? 回答1: In this case the static_cast<> is an 'explicit type conversion. the standard has this to say about integral conversions in 4.7/3 "Integral conversions": If the destination type is signed, the value is

问题 I have a list: ab = [1, 2, a, b, c] I did: strab = str(ab). So strab is now a string. I want to cast that string back into a list. How can I do that? 回答1: The easiest and safest way would be to use ast.literal_eval(): import ast ab = [1, 2, 'a', 'b', 'c'] # a list strab = str(ab) # the string representation of a list strab => "[1, 2, 'a', 'b', 'c']" lst = ast.literal_eval(strab) # convert string representation back to list lst => [1, 2, 'a', 'b', 'c'] ab == lst # sanity check: are they equal?

问题 I need to turn double into long preserving its binary structure, not number value. Just change type, but leave binary value as it is. Is there a native way to do it? 回答1: There is Double with to doubleToLongBits and doubleToLongRawBits. Javadoc is your friend. 来源： https://stackoverflow.com/questions/15065869/double-to-long-without-conversion-in-java

问题 I need to turn double into long preserving its binary structure, not number value. Just change type, but leave binary value as it is. Is there a native way to do it? 回答1: There is Double with to doubleToLongBits and doubleToLongRawBits. Javadoc is your friend. 来源： https://stackoverflow.com/questions/15065869/double-to-long-without-conversion-in-java

问题 I am wondering which is more efficient, using CStr() or object.toString(). The reason I ask this is because I though all that CStr() done was to invoke the .ToString() method on the object it was dealing with. But when recently using a generic method without any type constraints I had to use object.ToString() instead of CStr(object), the following is purely an example to illustrate the issue. Public Function IDFromObject(Of ID_TYPE)(ByVal value As ID_TYPE) As String Return value.ToString End