What string concatenation method to use for N number of iterations?

Question

If I want to concatenate string N the number of times, which method should I use?

Take this code as an example:

public static string Repeat(this string instance, int times)
{
        var result = string.Empty;

        for (int i = 0; i < times; i++)
            result += instance;

        return result;
}

This method can be called with a "time" set to 5 or 5000. Which method should I use?

string.join? StringBuilder? Just a standard string. Concat?

A similar function will be implemented in the commercial library, so I really need an “optimal” way to do this.

Answer 1

    public static string Repeat(this string instance, int times)
    {
        if (times == 1 || string.IsNullOrEmpty(instance)) return instance;
        if (times == 0) return "";
        if (times < 0) throw new ArgumentOutOfRangeException("times");
        StringBuilder sb = new StringBuilder(instance.Length * times);
        for (int i = 0; i < times; i++)
            sb.Append(instance);
        return sb.ToString();
    }

Answer 2

Stringbuilder ofcourse. , , .

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Answer 3

StringBuilder.

"result + = result;"

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Answer 4

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if(iterations < 30)
{
    CopyWithConcatenation();
}
else
{
    CopyWithStringBuilder();
}

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