I'm confused with the syntax of C#: what is the use of "+="?
+27
A:
The += syntax can be used in different ways:
SomeEvent += EventHandler;
Adds a handler to an event.
SomeVariable += 3;
Is equivalent to
SomeVariable = SomeVariable + 3;
SLaks
2010-03-22 14:54:08
Good answer. I would have spaced on the event handler aspect of this operator, despite knowing better.
Beska
2010-03-22 14:55:25
The event handler aspect is pretty much identical to the other aspects; all that's happening there is that the event/delegate object overrides the + operator.a += b is simply syntactic sugar for a = a + b. See http://msdn.microsoft.com/en-us/library/8edha89s.aspx, which states "Assignment operators cannot be overloaded, but +=, for example, is evaluated using +, which can be overloaded."
technophile
2010-03-22 15:01:06
@Technophile: Wrong. When outside the class (or always in C# 4.0), `instance.Event += handler` compiles to `instance.add_Event(handler);`
SLaks
2010-03-22 15:02:14
@SLaks Thank you for the clarification. They're conceptually identical, I had just misremembered the implementation.
technophile
2010-03-22 15:05:22
@Technophile: They're not entirely conceptually identical. In fact, it's a (subtle) breaking change: http://blogs.msdn.com/cburrows/archive/2010/03/18/events-get-a-little-overhaul-in-c-4-part-iii-breaking-changes.aspx
SLaks
2010-03-22 15:06:43
On an event, it calls the add method associated with the event. On a delegate field, however, it decomposed to SomeDelegate = SomeDelegate + AnotherDelegate and just concatenates the invocation lists.
Ben Voigt
2010-04-07 01:12:20
+4
A:
This is called a compound operator. There common to all languages I can thing of - Javascript, C, Java, PHP, .net, GL etc.
Like everyone has said, is a shorten'd version of value = value + 3.
There are multiple reasons for its use. Most obviously its quicker to write, easier to read and faster to spot errors with.
Most importantly, a compound operator is specifically designed not to require as must computation as the equivalent value = value + 3 I'm not totally sure why but the evidence is paramount.
Simply create a loop, looping for say 5,000,000 adding a value as you proceed. In two test cases, I know personally from Actionscript there is roughly an 60% speed increase with compound operators.
You also have the equivalent:
+= addition
-= subtraction
/= multiplication
*= multplication
%= modulus
and the lesser obvious
++ Plus one
-- Minus one
Hope it helps buddy.
Glycerine
2010-04-07 01:03:55
A:
note it is not necessarily always equivalent.
for ordinary variables, a+=a is, indeed, equivalent to a=a+a (and shorter!). for the odd variable which changes its state, not so much.
sreservoir
2010-04-25 15:18:47