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Return type of '?:' (ternary conditional operator)

Why does the first return a reference?

int x = 1;
int y = 2;
(x > y ? x : y) = 100;

While the second does not?

int x = 1;
long y = 2;
(x > y ? x : y) = 100;

Actually, the second did not compile at all - "not lvalue left of assignment".

How do I pass a variable by reference?

The Python documentation seems unclear about whether parameters are passed by reference or value, and the following code produces the unchanged value 'Original'

class PassByReference:
    def __init__(self):
        self.variable = 'Original'
        self.Change(self.variable)
        print self.variable

    def Change(self, var):
        var = 'Changed'

Is there something I can do to pass the variable by actual reference?

What is the difference between a soft reference and a weak reference in Java?

The title pretty much sums it.

What's the difference between the 'ref' and 'out' keywords?

I'm creating a function where I need to pass an object so that it can be modified by the function. What is the difference between:

public void myFunction(ref MyClass someClass)

and

public void myFunction(out MyClass someClass)

Which should I use and why?

What are the differences between a pointer variable and a reference variable in C++?

I know references are syntactic sugar, so code is easier to read and write.

But what are the differences?

Summary from answers and links below:

1. A pointer can be re-assigned any number of times while a reference can not be re-seated after binding.
2. Pointers can point nowhere (NULL), whereas reference always refer to an object.
3. You can't take the address of a reference like you can with pointers.
4. There's no "reference arithmetics" (but you can take the address of an object pointed by a reference and do pointer arithmetics on it as in &obj + 5).

To clarify a misconception:

The C++ standard is very careful to avoid dictating how a compiler must implement references, but every C++ compiler implements references as pointers. That is, a declaration such as:

int &ri = i;

if it's not optimized away entirely, allocates the same amount of storage as a pointer, and places the address of i into that storage.

So, a pointer and a reference both occupy the same amount of memory.

As a general rule,

• Use references in function parameters and return types to define useful and self-documenting interfaces.
• Use pointers to implement algorithms and data structures.

Interesting read:

• My alltime favorite C++ FQA lite.
• References vs. Pointers.
• An Introduction to References.
• References and const.

The located assembly's manifest definition does not match the assembly reference

I am trying to run some unit tests in a C# Windows Forms application (Visual Studio 2005) and I get the following error:

System.IO.FileLoadException: Could not load file or assembly 'Utility, Version=1.2.0.200, Culture=neutral, PublicKeyToken=764d581291d764f7' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)**

at x.Foo.FooGO()

at x.Foo.Foo2(String groupName_) in Foo.cs:line 123

at x.Foo.UnitTests.FooTests.TestFoo() in FooTests.cs:line 98**

System.IO.FileLoadException: Could not load file or assembly 'Utility, Version=1.2.0.203, Culture=neutral, PublicKeyToken=764d581291d764f7' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

I look in my references and I only have a reference to Utility version 1.2.0.203 (the other one is old).

Any suggestions on how I figure out what is trying to reference this old version of this DLL?

Besides, I don't think I even have this old assembly on my hard drive. Is there any tool to search for this old versioned assembly?

MongoDB relationships: embed or reference?

I'm new to MongoDB--coming from a relational database background. I want to design a question structure with some comments, but I don't know which relationship to use for comments: embed or reference?

A question with some comments, like stackoverflow, would have a structure like this:

Question
    title = 'aaa'
    content = bbb'
    comments = ???

At first, I want to use embeded comments (I think embed is recommended in MongoDB), like this:

Question
    title = 'aaa'
    content = 'bbb'
    comments = [ { content = 'xxx', createdAt = 'yyy'}, 
                 { content = 'xxx', createdAt = 'yyy'}, 
                 { content = 'xxx', createdAt = 'yyy'} ]

It clear, but I'm worried about this case: If I want to edit a specified comment, how do I get its content and its question? There is no _id to let me find one, nor question_ref to let me find its question. (I'm so newbie, that I don't know if there's any way to do this without _id and question_ref.)

Do I have to use ref not embed? Then I have to create a new collection for comments?

Pointer vs. Reference

What would be better practice when giving a function the original variable to work with:

unsigned long x = 4;

void func1(unsigned long& val) {
     val = 5;            
}
func1(x);

or:

void func2(unsigned long* val) {
     *val = 5;
}
func2(&x);

IOW: Is there any reason to pick one over another?

The type or namespace name could not be found [duplicate]

I have a C# solution with several projects in Visual Studio 2010. One is a test project (I'll call it "PrjTest"), the other is a Windows Forms Application project (I'll call it "PrjForm"). There is also a third project referenced by PrjForm, which it is able to reference and use successfully.

PrjForm references PrjTest, and PrjForm has a class with a using statement:

using PrjTest;

1. Reference has been correctly added
2. using statement is correctly in place
3. Spelling is correct
4. PrjTest builds successfully
5. PrjForm almost builds, but breaks on the using PrjTest; line with the error:

The type or namespace name 'PrjTest' could not be found (are you missing a using directive or an assembly reference?)

I've tried the following to resolve this:

1. Removed Resharper (since Resharper had no trouble recognizing the referenced project, I thought it might be worth a shot)
2. Removed and re-added the reference and using statement
3. Recreated PrjForm from scratch
4. PrjForm currently resides inside the PrjTest folder, I tried moving it to an outside folder
5. Loaded the solution on a different computer with a fresh copy of VS 2010

I have done my homework and spent far too long looking for an answer online, no solution has helped yet.

What else could I try?

Is there a difference between `==` and `is` in Python?

My Google-fu has failed me.

In Python, are the following two tests for equality equivalent (ha!)?

n = 5
# Test one.
if n == 5:
    print 'Yay!'

# Test two.
if n is 5:
    print 'Yay!'

Does this hold true for objects where you would be comparing instances (a list say)?

Okay, so this kind of answers my question:

L = []
L.append(1)
if L == [1]:
    print 'Yay!'
# Holds true, but...

if L is [1]:
    print 'Yay!'
# Doesn't.

So == tests value where is tests to see if they are the same object?

When to use References vs. Pointers

I understand the syntax and general semantics of pointers versus references, what I can't decide is when is it more-or-less appropriate to use references or pointers in an API?

Naturally some situations need one or the other (operator++ needs a reference argument), but in general I'm finding I prefer to use pointers (and const pointers) as the syntax is clear that the variables are being passed destructively.

E.g. in the following code:

void add_one(int& n) { n += 1; }
void add_one(int* const n) { *n += 1; }
int main() {
  int a = 0;
  add_one(a); // not clear that a may be modified
  add_one(&a); // a is clearly being passed destructively
}

With the pointer, it's always (more) obvious what's going on, so for APIs and the like where clarity is a big concern are pointers not more appropriate than references? Does that mean references should only be used when necessary (e.g. operator++)? Are there any performance concerns with one or the other?

EDIT (OUTDATED):

Besides allowing NULL values and dealing with raw arrays, it seems the choice comes down to personal preference. I've accepted the answer below that references Google's C++ Style Guide, as they present the view that "References can be confusing, as they have value syntax but pointer semantics.".

EDIT:

Due to the additional work required to sanitise pointer arguments that should not be NULL (e.g. add_one(0) will call the pointer version and break during runtime), it makes sense from a maintainability perspective to use references where an object MUST be present, though it is a shame to lose the syntactic clarity.

Android - reference a string in a string array resource with xml

I have been unable to find a solution for this.

What I'm trying to do: I have preferences where you can enable/disable what items will show up on the menu. There are 17 items. I made a string array in values/arrays.xml with titles for each of these 17 items.

I have preferences.xml which has the layout for my preferences file, and I would like to reference a single item from the string array to use as the title.

How, if it's possible, can I do this?

In the Android developer reference, I see how I can reference a single string with XML, but now how I can reference a string from an array resource in XML.

Thanks

Does JavaScript pass by reference?

Does JavaScript pass by references or pass by values? Here is an example from JavaScipt: The Good Parts. I am very confused about my parameter for the rectangle function. It is actually undefined, and redefined inside the function. There are no original reference. If I remove it from the function parameter, the inside area function is not able to access it.

Is it a closure? But no function is returned.

var shape = function (config) {
    var that = {};
    that.name = config.name || "";
    that.area = function () {
        return 0;
    };
    return that;
};
var rectangle = function (config, my) {
    my = my || {};
    my.l = config.length || 1;
    my.w = config.width || 1;
    var that = shape(config);
    that.area = function () {
        return my.l * my.w;
    };
    return that;
};
myShape = shape({
    name: "Unhnown"
});
myRec = rectangle({
    name: "Rectangle",
    length: 4,
    width: 6
});
console.log(myShape.name + " area is " + myShape.area() + " " + myRec.name + " area is " + myRec.area());

Could not load file or assembly or one of its dependencies

I'm having another of these "Could not load file or assembly or one of its dependencies" problems.

Additional information: Could not load file or assembly 'Microsoft.Practices.Unity, Version=1.2.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

I have no idea what is causing this or how I could debug it to find the cause.

I've done a search in my solution catalogs .csproj files, and every where I have Unity I have:

Reference Include="Microsoft.Practices.Unity, Version=2.0.414.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL"

Can't find any reference anywhere which goes against 1.2.0.0 in any of my projects.

Any ideas how I should go about solving this?

I would also appreciate tips on how to debug problems like this in general.

Why doesn't C# support the return of references?

I have read that .NET supports return of references, but C# doesn't. Is there a special reason? Why I can't do something like:

static ref int Max(ref int x, ref int y) 
{ 
  if (x > y) 
    return ref x; 
  else 
    return ref y; 
}