equality

问题 I have the following code: object val1 = 1; object val2 = 1; bool result1 = (val1 == val2);//Equals false bool result2 = val1.Equals(val2); //Equals true What's up with that? Is the only way to fix this to go with .Equals() method? 回答1: The operator == is static, not virtual, so the behaviour is determined by the static type and not the runtime type. The default implementation for == on objects of reference type is to compare the references (although types can implement a different behaviour,

问题 In Ruby 1.9.2 on Rails 3.0.3 , I'm attempting to test for object equality between two Friend (class inherits from ActiveRecord::Base ) objects. The objects are equal, but the test fails: Failure/Error: Friend.new(name: 'Bob').should eql(Friend.new(name: 'Bob')) expected #<Friend id: nil, event_id: nil, name: 'Bob', created_at: nil, updated_at: nil> got #<Friend id: nil, event_id: nil, name: 'Bob', created_at: nil, updated_at: nil> (compared using eql?) Just for grins, I also test for object

问题 In Ruby 1.9.2 on Rails 3.0.3 , I'm attempting to test for object equality between two Friend (class inherits from ActiveRecord::Base ) objects. The objects are equal, but the test fails: Failure/Error: Friend.new(name: 'Bob').should eql(Friend.new(name: 'Bob')) expected #<Friend id: nil, event_id: nil, name: 'Bob', created_at: nil, updated_at: nil> got #<Friend id: nil, event_id: nil, name: 'Bob', created_at: nil, updated_at: nil> (compared using eql?) Just for grins, I also test for object

问题 My question is not about floating precision. It is about why Equals() is different from == . I understand why .1f + .2f == .3f is false (while .1m + .2m == .3m is true ). I get that == is reference and .Equals() is value comparison. ( Edit : I know there is more to this.) But why is (.1f + .2f).Equals(.3f) true , while (.1d+.2d).Equals(.3d) is still false ? .1f + .2f == .3f; // false (.1f + .2f).Equals(.3f); // true (.1d + .2d).Equals(.3d); // false 回答1: The question is confusingly worded.

问题 This is a weird requirement I have. I know even my question is quite confusing. Here is what I want to know. I've two string variables. I need to do equality comparison of the datatype of the underlying value in the string variables. For ex. string firstVariable = "123"; // It contains integer value. i.e. I can convert it to integer value string secondVariable = "string" // It contains string value. Now I need to compare whether datatype of the underlying values of these two strings are same.

问题 How do you check if two NSMutableSets are equal ( same members, same number of members )? My implementation of isEqualToSet does not seem to be working. // members is a NSMutableSet of AUser objects // users is also a NSMutableSet of AUser objects, it is an attribute of instances of the AGroup class [[group valueForKey:@"users"] isEqualToSet:members] AGroup - users AUser - name (String) How do I check if the sets are equal by checking their name attributes? Sorry for my lack of knowledge, it

问题 I just read this nice answer given on how to compare floating-point values for equality. The following (slightly modified by me) is suggested instead of straight-forward comparison to 0: const double epsilon = 1e-5; double d = ...; if (Math.Abs(d) < epsilon) { // d is considered equal to 0. } My question is about the name of the variable epsilon 1) . Is "epsilon" the generally agreed-upon name for specifying the precision of floating-point numbers? (…which is the smallest discriminating

问题 I have an array of string like var a = ['a','a','a']; When I do comparison like a[0]==a[1]==a[2] it gives me result as false but when I change the value of array to ['1','1','1'] and do the same comparison like above the result will be true . Again when I change the input to ['9','9','9'] then above comparison is giving me result as false . Can anybody tell me the reason behind this behaviour in javascript ? 回答1: What you need is a[0]==a[1] && a[0]==a[2] In your case, when you are comparing [

问题 I understand the value of asserting [<StructuralEquality;StructuralComparison>] This statically forces equality and comparison constraints to be derived structurally, and have a nice side effect to warn if it can not Similarly [<ReferenceEquality>] forces the equality constraint to be satisfied using reference. Last NoComparison, NoEquality statically unsatisfy those constraints, with the benefit of catching errors as well. However I am unsure what the added value of CustomEquality,

问题 For clarity I will extract an excerpt from my code and use general names. I have a class Foo() that stores a DataFrame to an attribute. import pandas as pd import pandas.util.testing as pdt class Foo(): def __init__(self, bar): self.bar = bar # dict of dicts self.df = pd.DataFrame(bar) # pandas object def __eq__(self, other): if isinstance(other, self.__class__): return self.__dict__ == other.__dict__ return NotImplemented def __ne__(self, other): result = self.__eq__(other) if result is