When do you use the “this” keyword? [closed]

Answer 1

There are several usages of this keyword in C#.

1. To qualify members hidden by similar name
2. To have an object pass itself as a parameter to other methods
3. To have an object return itself from a method
4. To declare indexers
5. To declare extension methods
6. To pass parameters between constructors
7. To internally reassign value type (struct) value.
8. To invoke an extension method on the current instance
9. To cast itself to another type
10. To chain constructors defined in the same class

You can avoid the first usage by not having member and local variables with the same name in scope, for example by following common naming conventions and using properties (Pascal case) instead of fields (camel case) to avoid colliding with local variables (also camel case). In C# 3.0 fields can be converted to properties easily by using auto-implemented properties.

Answer 2

Any time you need a reference to the current object.

One particularly handy scenario is when your object is calling a function and wants to pass itself into it.

Example:

void onChange()
{
    screen.draw(this);
}

Answer 3

I tend to underscore fields with _ so don't really ever need to use this. Also R# tends to refactor them away anyway...

Answer 4

this on a C++ compiler

The C++ compiler will silently lookup for a symbol if it does not find it immediately. Sometimes, most of the time, it is good:

• using the mother class' method if you did not overloaded it in the child class.
• promoting a value of a type into another type

But sometimes, You just don't want the compiler to guess. You want the compiler to pick-up the right symbol and not another.

For me, those times are when, within a method, I want to access to a member method or member variable. I just don't want some random symbol picked up just because I wrote printf instead of print. this->printf would not have compiled.

The point is that, with C legacy libraries (§), legacy code written years ago (§§), or whatever could happen in a language where copy/pasting is an obsolete but still active feature, sometimes, telling the compiler to not play wits is a great idea.

These are the reasons I use this.

(§) it's still a kind of mystery to me, but I now wonder if the fact you include the <windows.h> header in your source, is the reason all the legacy C libraries symbols will pollute your global namespace

(§§) realizing that "you need to include a header, but that including this header will break your code because it uses some dumb macro with a generic name" is one of those russian roulette moments of a coder's life

Answer 5

When you are many developers working on the same code base, you need some code guidelines/rules. Where I work we've desided to use 'this' on fields, properties and events.

To me it makes good sense to do it like this, it makes the code easier to read when you differentiate between class-variables and method-variables.

Answer 6

You should not use "this" unless you absolutely must.

There IS a penalty associated with unnecessary verbosity. You should strive for code that is exactly as long as it needs to be, and no longer.