self-reference

问题 Consider the following sscce public enum Flippable A (Z), B (Y), Y (B), Z (A); private final Flippable opposite; private Flippable(Flippable opposite) { this.opposite = opposite; } public Flippable flip() { return opposite; } } This doesn't compile, because Z and Y haven't been declared to be allowed to be arguments of A and B 's constructor. Potential solution 1: Hardcoded Methods public enum Flippable { A { public Flippable flip() { return Z; } }, B { public Flippable flip() { return Y; } }

问题 If I define a function: def f(x): return x+3 I can later store objects as attributes of the function, like so: f.thing="hello!" I would like to do this from inside the code of the function itself. Problem is, how do I get a reference to the function from inside itself? 回答1: The same way, just use its name. >>> def g(x): ... g.r = 4 ... >>> g <function g at 0x0100AD68> >>> g(3) >>> g.r 4 回答2: If you are trying to do memoization, you can use a dictionary as a default parameter: def f(x, memo={}

问题 I have a data.table as follows set.seed(5) x <- data.table(x=sample(1:20,15)) > x x 1: 5 2: 14 3: 17 4: 20 5: 2 6: 11 7: 8 8: 15 9: 12 10: 16 11: 3 12: 18 13: 10 14: 4 15: 13 and I would like to start at 1 and cumulate values iteratively such that the value of cumsum() determines the next number to be added to the sum. In the example I want to add the first value of x , here 5, then jump to value number 5 and add that, here 2, then jump to value number 5+2=7 , here 8, then value number 5+2+8

问题 In the source table, there are two columns as following snapshot shows: Then for destination table, it should be something like this: ( "DimLocationKey" is auto-generated surrogate key ) How could I achieve self-referencing effect in SSIS? I tried following approach but it's not working because there would be no matches in the lookup. 回答1: If the column is nullable, then you could load the unique values for location_ID and then have a secondary process come back through and take care of

问题 I'm attempting to set this up using code first in entity framework and am running into difficulty. To describe what i'm trying to accomplish: Have an entity of Product. This product optionally may have one or more related "child" products. A product can be the child to one or more parent products. when I go to generate a controller tied to the model class "Product", i'm getting an error: (updated, more specific, matches code below) There was an error running the selected code generator:

问题 I have this example code: var foo = { self: this, init: function(){ self.doStuff(); }, doStuff: function(){ alert('doing stuff'); } } foo.init(); Why the refence "self" doesn't work? Thanks! 回答1: Following up on Qeuntin's response you would use the following to achieve what you're looking for var foo = { self: false, init: function(){ self = this self.doStuff(); }, doStuff: function(){ alert('doing stuff'); }, } EDIT: Since it's been pointed out that whilst this solves OP's problem (i.e it

问题 I have the following scenario in my database. It is a record of Studies and those studies have other studies as prerequisites. In my DB design, it looks like this: And my code looks something like this: public class Study { public int ID { get; set; } public string Topic { get; set; } public byte TypeID { get; set; } public virtual StudyType Type { get; set; } public bool Deprecated { get; set; } public virtual ICollection<Study> Prerequisites { get; set; } } public class StudyType { public

问题 How can I get a reference to a module from within that module? Also, how can I get a reference to the package containing that module? 回答1: import sys current_module = sys.modules[__name__] 回答2: If you have a class in that module, then the __module__ property of the class is the module name of the class. Thus you can access the module via sys.modules[klass.__module__] . This is also works for functions. 回答3: One more technique, which doesn't import the sys module, and arguably - depends on

问题 I came to a problem with interfaces in a program I'm making. I want to create a interface which have one of its methods receiving/returning a reference to the type of the own object. It was something like: public interface I { ? getSelf(); } public class A implements I { A getSelf() { return this; } } public class B implements I { B getSelf() { return this; } } I can't use an "I" where it's a "?", because I don't want to return a reference to the interface, but the class. I searched and found

问题 I'm trying to implement a self-referential many-to-many relationship using declarative on SQLAlchemy. The relationship represents friendship between two users. Online I've found (both in the documentation and Google) how to make a self-referential m2m relationship where somehow the roles are differentiated. This means that in this m2m relationships UserA is, for example, UserB's boss, so he lists him under a 'subordinates' attribute or what have you. In the same way UserB lists UserA under