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Description
Background and motivation
As far as I understand we could benefit in performance in case of AppendJoin with custom string representation of joined collection values representation if we build that representation by hand instead of creating new string for each element.
For example the following code creates new string for each iteration:
sb.AppendJoin(" ", context.Variables.Select(t => $"${t.Name}: {t.Type}"));API Proposal
namespace System.Text;
public class StringBuilder
{
public static StringBuilder AppendJoin<T>(string separator, IEnumerable<T> values, Action<StringBuilder, T> appendFunc);
public static StringBuilder AppendJoin<T>(char separator, IEnumerable<T> values, Action<StringBuilder, T> appendFunc);
}API Usage
sb.AppendJoin(" ", context.Variables,
(sb, t) => sb
.Append("$")
.Append(t.Name)
.Append(": ")
.Append(t.Type));
// or
sb.AppendJoin(" ", context.Variables, (sb, t) => sb.Append($"${t.Name}: {t.Type}"));Alternative Designs
Possibly some interpolated string API (e.g. like Append(StringBuilder+AppendInterpolatedStringHandler)) could do
namespace System.Text;
public class StringBuilder
{
public static StringBuilder AppendJoin<T>(string separator, IEnumerable<T> values, Func<T, StringBuilder+AppendInterpolatedStringHandler> toStringFunc);
}Risks
No response