Performance cost of creating array of constants as function argument

Question

Here is an example. Suppose I want to split a string on multiple delimiters using the String.Split() method. Here's what I would write in C#:

    myString.Split(new [] { ',', ';', ':' }, StringSplitOptions.RemoveEmptyEntries)

Now, the actual argument to the function is an array of constant (i. e. known at the compile/JIT time) values, and this array is, at the least syntactically, allocated every time the expression is evaluated.

Is there a magic (or optimization, if you do not believe in magic) in the CLR that will avoid allocating and initializing the array every time, or is the array really constructed every time this code is executed? I am asking both in a broad sense about the CLR in general, if there is such a thing, and also narrowly about the Microsoft's implementation in .NET in particular.

Christian.K · Accepted Answer · 2015-01-05 13:47:42Z

1

No, the array will be allocated every time. Probably not a big deal in average situations, but could pretty well be in a tight loop, or if called very often (like on a busy server, etc.).

In summary, if you suffer here, it is best to put your typical delimiter arrays in a helper class, like so:

public static class SplitHelpers 
{
   public static readonly char[] Comma = { ',' };
   public static readonly char[] Stuff = { ',', ':', ';' };
   // etc.
}

Then use these from your call sites:

myString.Split(SplitHelpers.Stuff, StringSplitOptions.RemoveEmptyEntries)

Credit, where credit is due, Marc Gravell has written an pretty good blog post about this issue. I suggest you read that for more details.

answered Jan 5, 2015 at 13:47

Christian.K

49.6k10 gold badges108 silver badges155 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Performance cost of creating array of constants as function argument

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related