equality

#!/usr/bin/env perl use warnings; use 5.12.2; my $c = 'f'; # could be a number too if ( $c eq 'd' || $c == 9 ) { say "Hello, world!"; } What is the best way, to avoid the 'Argument "f" isn't numeric in numeric eq (==) at ./perl.pl line 7.'-warning? I suppose in this case I could use "eq" two times, but that doesn't look good. Not sure why you want to avoid the warning. The warning is telling you that there's a potential problem in your program. If you're going to compare a number with a string that contains unknown data, then you're either going to have to use 'eq' for the comparison or clean

Consider this snippet: class SomeClass(object): def __init__(self, someattribute="somevalue"): self.someattribute = someattribute def __eq__(self, other): return self.someattribute == other.someattribute def __ne__(self, other): return not self.__eq__(other) list_of_objects = [SomeClass()] print(SomeClass() in list_of_objects) set_of_objects = set([SomeClass()]) print(SomeClass() in set_of_objects) which evaluates to: True False Can anyone explain why the 'in' keyword has a different meaning for sets and lists? I would have expected both to return True, especially when the type being tested

System.Collections.IStructuralEquatable and System.Collections.IStructuralComparable were added in .NET 4, but why aren't they generic, like IEquatable<T> and IComparable<T> ? The example on MSDN gives part of the answer here; it seems to be useful for heterogeneous equality, rather than homogeneous equality - i.e. for testing whether two objects (/values) of potentially different types should be considered equal. In such scenarios, it is extremely likely that the calling code is dealing with object (to represent heterogeneous data). And generic methods don't play nicely then. 来源： https:/

I have made heavy use of case classes in my code, replying on the underlying equality definitions of case class to behave correctly. Then now I found that I need to add another field member to a case class. So if I add a var field member in case class, will it mess up the equality attributes for the case class? If 1 is yes, then what if I just change the var field value once, after that, no any reassignment will happen, before the case class goes into any collections or do equality comparison, will that still mess up the equality behaviors? Case class equality is based solely on its primary

Is there a tool or library to find duplicate entries in a Collection according to specific criteria that can be implemented? To make myself clear: I want to compare the entries to each other according to specific criteria. So I think a Predicate returning just true or false isn't enough. I can't use equals . It depends on the semantic of the criterion: If your criterion is always the same for a given class, and is inherent to the underlying concept , you should just implement equals and hashCode and use a set. If your criterion depend on the context , org.apache.commons.collections