Substring implementation via Span

Question

How would an implementation of a SubstringFromStart method look like when Span<T> should be leveraged? Assuming substringLength <= input.Length:

 ReadOnlySpan<char> span = input.AsSpan().Slice(0, substringLength);
 return new string(span.ToArray());

Is this the way to go? Is there a better, more concise way than new string(span.ToArray())?

Answer 1

Is this the way to go?

No, using Span<T> is useless here, since you need a character array for the string constructor (there is none that accepts a Span<char> yet).

You would benefit using Span<T> here if:

• You would return the Span<char>, rather than a string. Then you wouldn't need the string allocation;
• You receive a Span<char> as input and you never need to materialize it to an array, or you wouldn't need a intermediate materialization (when passing it into the method for example).