Using The u8 String Literal

A number of processing APIs and modules operate on byte arrays rather than discrete structures like strings.

You will, therefore, find yourself often doing the following:

// Get a byte array of the data
var data = Encoding.Default.GetBytes("This is my raw data");

Two things are happening here:

1. Memory is allocated to store the byte array
2. The process of converting the string to a byte array is carried out, and the result is stored in the new memory. This is called an allocation.

This is a fairly common operation, especially when it comes to the ASP.NET engine, which deals a lot with strings and byte arrays.

There has been an improvement on this at compile time - the UTF 8 string literal.

The previous code can be written as follows:

var data = "This is my raw data"u8;

There are two important things to note here:

• The u8 immediately after the closing quotes is a UTF 8 string literal, instructing the compiler and runtime on what to do with the data. We have met integer literals before
• The variable data contains not a byte array but a ReadOnlySpan<byte>. This is a faster technique of accessing data that avoids allocations. This is string data in UTF 8 encoding.

The Span and ReadOnlySpan have such benefits for performance and memory reasons that an increasing number of APIs that used to take byte arrays or strings now have overloads that accept ReadOnlySpans.

For example, the API that writes data to a file takes both a byte array and a ReadOnlySpan<byte> as a parameter, File.WriteAllBytes() in addition to the file name.

So, we can modify our first example to write the data to a file as follows:

// Get a byte array of the data
var data = Encoding.Default.GetBytes("This is my raw data");

// Ask the OS for a temporary file name
var temporaryFileName = Path.GetTempFileName();

// Write data to disk
File.WriteAllBytes(temporaryFileName, data);

In the code, data is a byte array.

We can modify the second example that uses a string literal as follows:

// Get a byte ReadOnlySpan<byte> of the data
var data = "This is my raw data"u8;

// Ask the OS for a temporary file name
var temporaryFileName = Path.GetTempFileName();

// Write data to disk
File.WriteAllBytes(temporaryFileName, data);

The code is virtually identical, but you can see that the API to write the data to disk now is taking a ReadOnlySpan<byte> rather than a byte array.

Happy hacking!