JavaScript 中的逻辑运算符 && 和它的 C# 等效

Question

In JavaScritp operator && can be used to invoke functions like this

possibleNull && possibleNull.do()

This executes do() method of the possibleNull object only of possibleNull object is not null. This can be handled by?. operator. However I coud not find C# alternative for

let foo = _fooProvider.GetFoo();
return foo && processFoo(foo);

In "left && right" epxression in JS, when left variable be evaluated to "true" (generaly not null -> there are more cases in JS though), right variable is returned (or executed).

I know about C# alternative for || JS operator that works almost the same (?? operator). Is there also a counterpart for &&?

Edit: I know that && can be short-circuited when both operands are bool. However in JS you can have right side that returns something else than bool. Left side in JS is indeed automaticaly converted to bool by the interpreter, yet righ side is just evaluated and returned as such.

I'd like to achieve something like

public Foo Do(Foo arg)
...
var foo = _fooProvider.GetFoo();
return foo != null && Do(foo);

Without using if-else or ternary operator.

Answer 1

What you are really asking about is logical operator "short-circuiting" where if the first condition in a multiple condition test fails, the statement processing stops.

C# works just as JavaScript does in this regard:

& Logical AND
&& Logical AND with short-circuiting
| Logical OR
|| Logical OR with short-circuiting

Answer 2

If you want an OO solution to your problem. Why not implement the null patterns?

I do not know if Foo has an interface in your situation or if that is reasonabily implementable.

But instead of littering your code with null checks and maybe have all that null behaviour loatering around. (like if object is null log something)

Do something like

public interface IFoo { void Do(); }

public class Foo : IFoo { void Do() { /* all that stuff you wanna do */ } }

public class NullFoo : IFoo { void Do { /*log that do cannot be called on nullFoo because Foo with Code X could not be found */ } }

Foo probably comes from a repo or factory, when you see it cannot be instantiated. Instead of having the client check for null, just return NullFoo, let it call Do which does nothing or log that it could not be found, and go on with its day:)

Hope this helps!

Answer 3

The && operator in C# works just like in JavaScript, but only for bool operands. You can have operands of any type in JavaScript.

JavaScript uses type coercion - it assigns boolean values (true/false) to non-bool variables.

0               -> false
non-0 number    -> true
[]              -> false
non-empty array -> true
undefined, null -> false
{}              -> true

x && y in JS works like this: If x coerces to false, x is returned. If x coerces to true, y is returned.

C# works the same, just with bool operands only. If x is false, x (false) is returned. If x is true and y is false, y (false) is returned. If x is true and y is true, y (true) is returned.

Now this isn't really useful for writing short code like in JS. Probably the best you can do is if (foo != null) processFoo(foo) or ternary foo == null? getNewFoo(): processFoo(foo) foo == null? getNewFoo(): processFoo(foo) .