C＃比较速记

Question

I have this code:

    if (y == a && y == b && y == c && y == d ...)
    {
        ...
    }

Is there some form of shorthand so that I can rewrite it as something like this?

    if(y == (a && b && c && d ...))
    {
        ...
    }

The functionality should be exactly the same. I'm just looking for something that looks less confusing.

EDIT Sorry for not clarifying, all the variables are integers. I'm looking for a shorter way to ensure that a , b , c , d , ... all equal y .

Answer 1

The closest you're going to get (without implementing your own kind of mechanism):

if (new[] { a, b, c, d }.All(value => y == value))
    // ...

Answer 2

No , there isn't anything that will simplify your code without outweighing the readability benefits with a big performance penalty.

---

Edit: High-performance solution

If you're desperate enough to try a high-performance solution, here's one:

(Update: Apparently I was wrong in thinking you can use generics with varargs; you apparently can only hard-code the types. So I changed the type below to int instead, but the same code applies.)

static bool AllEqual(int value, __arglist)
{
    for (var ai = new ArgIterator(__arglist); ai.GetRemainingCount() > 0; )
    {
        var next = __refvalue(ai.GetNextArg(typeof(int).TypeHandle), int);
        if (!value.Equals(next)) { return false; }
    }
    return true;
}

Then try calling it with:

//...
bool equal = AllEqual(1, __arglist(1, 1, 1));

Warning: People will probably yell at you for doing this, so use it at your own risk. :)

Answer 3

Slightly more readable (in my opinion) is:

if ((y == a) && (y == b) && (y == c) && (y == d) ...)

but I don't believe there's anything in the base language for this.

If you really want something like what you propose, that's what functions are for, something like:

if (isSetToAll (y, a, b, c, d, ...))

but you might want to be careful on the performance front.

---

One thing may be of use to you if that's being done in a loop where a/b/c/d/... are invariant (in other words, where only y is changing).

Check the equality for the invariants outside the loop:

if ((a == b) && (a == c) && (a == d) ...)

because, if that's not the case, then y can never be equal to all of them. Then, inside the loop, just do:

if (y == a)

The fact that you already know that all the non- y variables are equal to each other means that you only need to check y against one of them.

But, since I haven't seen your complete code, I'm not sure if it will be useful to you.

---

I should mention that, while verbose, there's nothing actually unreadable about your original code, especially if it's formatted nicely. Even the behemoth:

if ((y == a) && (y == b) && (y == c) && (y == d) &&
    (y == e) && (y == f) && (y == g) && (y == h) &&
    (y == i) && (y == j) && (y == k) && (y == l) &&
    (y == m) && (y == n) && (y == o) && (y == p) &&
    (y == q) && (y == r) && (y == s) && (y == t) &&
    (y == u) && (y == v) && (y == w) && (y == x))
{
    ...
}

is readable (though I'm not a big fan of terse variable names).

Of course, at that point, you may want to look into using arrays with loops rather than singular variables.

Answer 4

No, there isn't. Stick with what you have.

Well, you could write a public static bool AllEqual<T>(params T[] values) (maybe with overloads for 2/3/4/5 operands to avoid the array creation), but I'm not sure it is worth it most times.

Answer 5

Try this:

Assuming you're comparing strings

IList<string> valuesToCompare = new List<string> { "a", "b", "c", "d" };

if (valuesToCompare.Any(valueToCompare => valueToCompare != y)) 
       //If there is any value that is not equal to y
       //Do something

Answer 6

new[] { a, b, c, d }.Contains(y)

Answer 7

Although it's impossible to be sure, I'd look at your overall code structure and see if there isn't just a better way to handle that whole area.

Any time you have a pattern that repeats like that, you will probably have to modify it a lot. Chances are that you will need to add a new q==y or change something eventually.

A lot of people here were concerned with performance, but it's much more important to make sure your code is maintainable and understandable and properly factored.

As a total guess, I'd say that your a,b,c,d variables should all be a member of 4 different objects, ax, bx, cx, dx what do a,b,c,d represent? They can't just be arbitrary numbers, they are prices or pixel locations or weights of elements--something! I can't imagine a condition where you'd have exactly 4 and never 5 or 3 of something.

Anyway, whatever it represents, there are probably other things associated with it--a name, size, color, control index--whatever.

In general I'd look at a higher level for a fix to this problem. I'd say at least a,b,c & d should be something defined outside the program, either in a data file or database.

Answer 8

For if (y == a && y == b && y == c && y == d) , use:

if ( y == a == b == c == d) { //code here }

For if (y == a || y == b || y == c || y == d) and y is a simple type or string, use:

switch(y)
{
   case a:
   case b:
   case c:
   case d:
     //your code here
     break;

}

Answer 9

   bool  x=true ,y=true, z=true, p = true;

    if (x == (y == z == p)) //true

    x = false;
    if (x == (y == z == p)) //false