CODEWITHSUNDEEP
c#constants
pencilCake
pencilCake

Reputation: 53223

Is there any benefit to declare a constant in a local scope in C#?

Is there any benefit to declare a local variable as "const" if I know that I won't be chaning its value?

Thanks,

Upvotes: 8

Views: 618

Answers (7)

John Warlow
John Warlow

Reputation: 2992

Declaring the variable const will also allow the compiler to do optimisation - instead of say allocating an int on the stack and placing its value there, the compiler may just use the value directly with your code

ie The following:

const int test = 4;
DoSomething(test);

Could be compiled as

DoSomething(4);

by the compiler

Edit: Reply to "constant propagation" as the comments box has size limit

Using ildasm to check betweeen const and none const for release with optimisation:

The code

int test = 4;
Console.WriteLine(test*2);

Compiles to 

.method private hidebysig static void  Main(string[] args) cil managed
{
  .entrypoint
  // Code size       11 (0xb)
  .maxstack  2
  .locals init ([0] int32 test)
  IL_0000:  ldc.i4.4
  IL_0001:  stloc.0
  IL_0002:  ldloc.0
  IL_0003:  ldc.i4.2
  IL_0004:  mul
  IL_0005:  call       void [mscorlib]System.Console::WriteLine(int32)
  IL_000a:  ret
} // end of method Program::Main

While

const int test = 4;
Console.WriteLine(test*2);

gets optimised to

.method private hidebysig static void  Main(string[] args) cil managed
{
  .entrypoint
  // Code size       7 (0x7)
  .maxstack  8
  IL_0000:  ldc.i4.8
  IL_0001:  call       void [mscorlib]System.Console::WriteLine(int32)
  IL_0006:  ret
} // end of method Program::Main

This is using 2010 in release with optimisations.

I did a search to learn more about constant propagation and while posible, the current compiler doesn't do this as mentioned here

Upvotes: 5

Dan Bryant
Dan Bryant

Reputation: 27495

I like to do this when I'm passing a boolean flag indicator to a method:

const bool includeFoo = true;
int result = bar.Compute(10, includeFoo);

This is more readable for me than a simple true/false, which requires reading the method declaration to determine the meaning.

Upvotes: 3

abatishchev
abatishchev

Reputation: 100248

Depending on case of use..

For example,

void Foo()
{
    const string xpath = "//pattern/node";

    new XmlDocument().SelectNodes(xpath);
}

in this case I think const declaration is meaningless

Upvotes: 0

Paul Hadfield
Paul Hadfield

Reputation: 6136

Further to the valid answers, not only do you tell the compiler that the value won't be changing, you quickly tell anyone else that will be looking at your code.

Upvotes: 1

Spooks
Spooks

Reputation: 7177

You would usually use a const throughout your entire solution. But the benefits for using in a local scope, would be that you know some place else in your scope you won't be changing it. And also if someone else is working on this code, they will know not to change it as well. This makes your program more maintainable, because you need to maintain only the const (even if its just in a local scope)

Upvotes: 6

Jake Pearson
Jake Pearson

Reputation: 27717

Declaring the local as const will let the compiler know you intention so you won't be able to change the value of your variable elsewhere in your function.

Upvotes: 2

user151323
user151323

Reputation:

Yes. You will protect your code from accidentally changing this variable.

Upvotes: 3

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