[API Proposal]: Stringbuilder.Replace(ROS oldValue, ROS newValue, int index, int count)

[CodingMadness]

Background and motivation

I am operating a lot with spans and slicees and I would super like to not get forced to write-out the span to a string by "builder.ToString()", if possible.

It would save tremendous allocations cause when working in game dev /graphics related stuff , the amount of calls which happen per second make up a significant GC-pressure, so would be nice to avoid that.

API Proposal

  public StringBuilder Replace(ReadOnlySpan<char> oldValue, ReadOnlySpan<char> newValue, int startIndex, int count)
  public StringBuilder Replace(ReadOnlySpan<char> oldValue, ReadOnlySpan<char> newValue)

API Usage

string input = "Hello world";

ROS charSpan = bigString.Slice(0, 5);
ROS replacer = stackalloc char[] {'d', 'e', 'a', 'r'};
StringBuilder builder = new(input);

builder.Replace(charSpan, replacer);

var output = builder.ToString(); // --> dear world

Alternative Designs

Due to backward compatibility, it would be only an option to add a new API.

Risks

AFAIK none.

[ghost]

Tagging subscribers to this area: @dotnet/area-system-runtime
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Background and motivation

I am operating a lot with spans and slicees and I would super like to not get forced to write-out the span to a string by "builder.ToString()", if possible.

It would save tremendous allocations cause when working in game dev /graphics related stuff , the amount of calls which happen per second make up a significant GC-pressure, so would be nice to avoid that.

API Proposal

  public StringBuilder Replace(ReadOnlySpan<char> oldValue, ReadOnlySpan<char> newValue, int startIndex, int count)
  public StringBuilder Replace(ReadOnlySpan<char> oldValue, ReadOnlySpan<char> newValue)

API Usage

string input = "Hello world";

ROS charSpan = bigString.Slice(0, 5);
ROS replacer = stackalloc char[] {'d', 'e', 'a', 'r'};
StringBuilder builder = new(input);

builder.Replace(charSpan, replacer);

Alternative Designs

Due to backward compatibility, it would be only an option to add a new API.

Risks

AFAIK none.

Author:	Shpendicus
Assignees:	-
Labels:	api-suggestion, area-System.Runtime
Milestone:	-

[CodingMadness]

May I know if this API proposal could be something for .net 8 release?

thx in advance and coolio work you have put in this .NET thing!

[stephentoub]

These won't make .NET 8, which is all but done at this point.

But the proposal looks reasonable for .NET 9. I've marked it as ready for review. Thanks.

[CodingMadness]

These won't make .NET 8, which is all but done at this point.

But the proposal looks reasonable for .NET 9. I've marked it as ready for review. Thanks.

Any chance btw to adapt this proposal also for the "AppendJoin()" and "AppendFormat()" methods which still take only string, considering that StringBuilder is used most of the time in high allocation-pressured code , I assume this could be a reasonable adaption aswell.

[stephentoub]

These won't make .NET 8, which is all but done at this point.
But the proposal looks reasonable for .NET 9. I've marked it as ready for review. Thanks.

Any chance btw to adapt this proposal also for the "AppendJoin()" and "AppendFormat()" methods which still take only string, considering that StringBuilder is used most of the time in high allocation-pressured code , I assume this could be a reasonable adaption aswell.

Please open a separate issue with supporting details, real examples of where it'd be helpful, etc. Thanks.

[CodingMadness]

These won't make .NET 8, which is all but done at this point.
But the proposal looks reasonable for .NET 9. I've marked it as ready for review. Thanks.

Any chance btw to adapt this proposal also for the "AppendJoin()" and "AppendFormat()" methods which still take only string, considering that StringBuilder is used most of the time in high allocation-pressured code , I assume this could be a reasonable adaption aswell.

Please open a separate issue with supporting details, real examples of where it'd be helpful, etc. Thanks.

Not gonna lie I have already had your answer in mind when i was typing, so thats on me ^^.

[TheMaximum]

Just to see how easy it would be to implement something like this, I've already attempted an implementation (see commit below). Was able to change the current implementation with string as arguments to one that takes ReadOnlySpan<char>. The string-methods can then call the ROS one with .AsSpan(). Tests still work, as do the added ones for the ROS variants. Was looking to see if I can somehow benchmark the implementations, but I can't figure out how to run these against the self-built runtime.

Not sure if it's the way you want to go with it, but was educational for me either way.

---

Provided that this gets through the review meeting, I'd be interested to take a crack at this issue.

Apologies for the original response below, I misunderstood what you're trying to do (a Replace method on StringBuilder, not a Replace method for a ReadOnlySpan<char> in general).

---

I noticed that a method (ReplaceCore, see below) already exists that accepts ReadOnlySpan<char> as arguments.
It currently returns a string?, but uses a ValueStringBuilder, which could also return the value as ReadOnlySpan<char>.
The ValueStringBuilder doesn't seem to convert to StringBuilder, but maybe a ReadOnlySpan<char> might work as return type as well? In that case ReplaceCore could return the ValueStringBuilder and the calling methods can then decide to return it with .ToString() or .AsSpan().

Don't know if this is the path to take, and other pointers in the right direction are welcome if you're happy for me to have a look at it.

runtime/src/libraries/System.Private.CoreLib/src/System/String.Manipulation.cs

Lines 1110 to 1116 in 8e1e6f5

	private static string? ReplaceCore(ReadOnlySpan<char> searchSpace, ReadOnlySpan<char> oldValue, ReadOnlySpan<char> newValue, CompareInfo compareInfo, CompareOptions options)
	{
	Debug.Assert(!oldValue.IsEmpty);
	Debug.Assert(compareInfo != null);
	var result = new ValueStringBuilder(stackalloc char[StackallocCharBufferSizeLimit]);

[bartonjs]

Video

Looks good as proposed.

namespace System.Text;

partial class StringBuilder
{
   public StringBuilder Replace(ReadOnlySpan<char> oldValue, ReadOnlySpan<char> newValue, int startIndex, int count);
   public StringBuilder Replace(ReadOnlySpan<char> oldValue, ReadOnlySpan<char> newValue);
}

[CodingMadness]

will this be ready for .NET 9 or maybe earlier?

[adamsitnik]

will this be ready for .NET 9 or maybe earlier?

It will be part of .NET 9. We don't backport new features to versions that were already shipped (.NET 8 RTM was shipped 2 weeks ago)