Crash-Course: Spans in C#
Spans are special structs in .NET Core designed to provide pointer-like constructs in safe, managed contexts. This allows array and buffer manipulation similar to how how they’re done in C++, C and Pascal and with comparable performance.
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- Arrays implicitly casts to spans
byte[] byteArr = …;
// implicit cast
ReadOnlySpan<byte> span = byteArr;
Span<byte> span2 = byteArr;
NOTE
- use ReadOnlySpan if you never need to change a value
- only use Span if you need to change a value
2. Spans encapsulate “offset and length” as a well as pointer. Thus method signatures like:
void SomeMethod(byte[] arr, int offset, int length)
…
SomeMethod(myArr, myOffset, myLength)
become
void SomeMethod(ReadOnlySpan<byte> arr)
…
SomeMethod(myArr.AsSpan(myOffset, myLength))
To get a sub-span within a span, use
mySpan.Slice(newOffset, newLength)
myArray.AsSpan(newOffset, newLength)
Length argument can be omitted and inferred as the remainer of the array after offset.
mySpan.Slice(newOffset); // from newOffset to end of
myArr.AsSpan(1); // this gets everything after first byte
3. In unsafe contexts,to get byte* of a span, use
byte *p = &mySpan.GetPinnableReference();
Learn more at: https://docs.microsoft.com/en-us/archive/msdn-magazine/2018/january/csharp-all-about-span-exploring-a-new-net-mainstay
