More C# 7 goodness – Span of T – Span

Introduction

With C# 7.2 we got a new type: Span<T>. So, what is Span? Span is a new value type that enables us to work and manage any type that represents a contiguous chunk of memory.

As Mads Torgersen has put it: Span is a window onto an existing chunk of memory. For instance a chunk of memory that array represents or any type that represents the span of variables of the same type. Span is simply pointing to existing memory. It doesn’t have its own memory.

Span<T> is a struct and it will NOT cause heap allocation.

Span<T> provides type-safe access to memory while maintaining the performance of arrays.

We can use Span with:

  • arrays
  • strings
  • stack allocation
  • native buffers

It is very useful because we can simply slice an existing chunk of memory and manage it, we don’t have to copy it and allocate new memory.

List of types that we can convert to Span<T>:

  • Arrays
  • Pointers
  • stackalloc
  • IntPtr

 

With ReadOnlySpan<T> we can convert all above and string:

  • Arrays
  • Pointers
  • stackalloc
  • IntPtr
  • string

 

Code

Pointing to existing array

Let’s see an example with array and Span:

That prints out all the numbers.

 

Using only slice of an array

We can also use a slice of that array:

This will only print out 3 values. Elements from index 1 to 3, with the element at index 3 included. Slice will not modify the array.

 

Span constructor

As we said, Span is only a window onto existing memory. Hence, if we want to use a Span constructor, we have to provide it with an array, or part of array or pointer to some piece of memory:

 

Creating new Span and copying elements from one Span to another

We can also copy elements to the new span. However, when we initialize new span we need to create a new array or give it existing one.

We will create a new array and copy elements from one span to another:

Destination span points out to completely new memory location and that’s why clearing the first span will not affect the destination span.

That prints out:

Clear and Fill

Span has methods available to clear the values of memory where it points to. For an array, it would reset all values to default ones.

We can also use fill to populate all elements with the same value.

 

ToArray and ToString

We can also create a new array or string from existing Span and that will actually create a new array or string in memory.

 

Disadvantages

Since Span is actually a struct and it does not inherit from IEnumerable, we can’t use LINQ against it. This is a big minus when compared to C# collections.

Span also has only limited number of methods available. It is really useful for saving memory but regarding manipulation of data that it points to we can’t do much.

Ibrahim Šuta

Software Engineer, Mentor and Consultant interested and specialising in ASP.NET Core, C#, JavaScript, Angular, React.js. Experienced in MeteorJS, Node.js, ASP.NET, Windows Forms and Web Forms as well.