Concatenating ReadOnlySpan<T>

There’s no add operator between Span<T>’s nor ReadOnlySpan<T>. But there are some new methods added to the standard library that now accepts these new types and give great value to them, especially when it comes to the <char> variants.

You can keep on using ReadOnlySpan<char> without the performance cost or memory allocations of creating intermediate strings just to build bigger strings.

StringBuilder.Append

StringBuilder.Append is the de-facto standard for concatenating +2 strings in an efficient way. If you’re working with ReadOnlySpan<char>, then you’d be delighted to know that the StringBuilder.Append method does have native support for them.

public sealed partial class StringBuilder
{
    public System.Text.StringBuilder? Append (ReadOnlySpan<char> value);
}
var builder = new StringBuilder();
builder.Append(new [] { 'a', 'b', 'c', 'd', 'e' }.AsSpan());
builder.Append("fghij".AsSpan());

Console.WriteLine(builder.ToString());
// abcdefghij

String.Concat

String.Concat is a marvelous example. An otherwise unused method (as you can simply add + strings together), but since .NET Core 3.0 you can pass it ReadOnlySpan<T>!

public sealed partial class String
{
    // Concat 2 ReadOnlySpan<char>'s
    public static string? Concat (ReadOnlySpan<char> str0, ReadOnlySpan<char> str1);
    // Concat 3 ReadOnlySpan<char>'s
    public static string? Concat (ReadOnlySpan<char> str0, ReadOnlySpan<char> str1, ReadOnlySpan<char> str2);
    // Concat 4 ReadOnlySpan<char>'s
    public static string? Concat (ReadOnlySpan<char> str0, ReadOnlySpan<char> str1, ReadOnlySpan<char> str2, ReadOnlySpan<char> str3);
}
var chars = new [] { 'a', 'b', 'c', 'd', 'e' }.AsSpan();
var text = "fghij".AsSpan();

Console.WriteLine(string.Concat(chars,text));
// abcdefghij
logo