[API Proposal]: Add string.ReplaceWhere for predicate-based replacement and removal

[yousefyahia828]

Background and motivation

Background and Motivation

string provides Replace overloads for replacing known values, but there is no built-in API for replacing or removing characters based on a predicate.

This is a common operation that currently requires manual iteration or LINQ. A dedicated API would improve readability while allowing for an efficient implementation.

API Proposal

Proposed API

namespace System;

public partial class String
{
    /// <summary>
    /// Replaces or removes all characters that satisfy the specified predicate.
    /// </summary>
    /// <param name="predicate">
    /// A function that determines whether a character should be replaced.
    /// </param>
    /// <param name="replacement">
    /// The replacement character. If <see langword="null"/>, matching characters are removed.
    /// </param>
    /// <returns>
    /// A new string with matching characters replaced or removed.
    /// </returns>
    public string ReplaceWhere(
        Func<char, bool> predicate,
        char? replacement = null);
}

API Usage

API Usage

string value = "abc123";

value.ReplaceWhere(char.IsDigit);
// "abc"

value.ReplaceWhere(char.IsDigit, '*');
// "abc***"

Alternative Designs

No response

Risks

No response

[dotnet-policy-service]

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

[MihaZupan]

A dedicated API would improve readability while allowing for an efficient implementation.

It is unlikely that any such API that takes a predicate could be efficient.

If you care about perf, you could use a helper such as this:

public static string ReplaceAny(this string text, SearchValues<char> values, char newValue)
{
    if (!text.ContainsAny(values))
        return text;

    return string.Create(text.Length, (text, values, newValue), static (span, state) =>
        state.text.AsSpan().ReplaceAny(span, state.values, state.newValue));
}

[Symbai]

There are many similar requests which have been closed before:
#40407
#29249
#24318
#41287

And most of them have been basically closed by this argument:

APIs additions on basic types (like string) have a high bar and have to add true value. Saving a few keystrokes is somewhat useful but it's low-impact and yet another thing customers have to learn. An example of the type of impact that would meet the bar for string would be saving customers from having to write an algorithm. Especially if it's logic they might need to implement frequently and which they're inclined to get wrong.