For others interested in the source of StringBuilder: https://github.com/mono/mono/blob/master/mcs/class/corlib/System.Text/StringBuilder.cs#L50 https://github.

For others interested in the source of StringBuilder: https://github.com/mono/mono/blob/master/mcs/class/corlib/System.Text/StringBuilder.cs#L50 https://github.com/mono/mono/blob/master/mcs/class/corlib/Sy... Note that the actual magic consists of internal methods in String.cs: - FormatHelper https://github.com/mono/mono/blob/master/mcs/class/corlib/System/String.cs#L1928 https://github.com/mono/mono/blob/master/mcs/class/corlib/Sy... - InternalSetChar https://github.com/mono/mono/blob/master/mcs/class/corlib/System/String.cs#L2585 https://github.com/mono/mono/blob/master/mcs/class/corlib/Sy... - CharCopy https://github.com/mono/mono/blob/master/mcs/class/corlib/System/String.cs#L3060 https://github.com/mono/mono/blob/master/mcs/class/corlib/Sy...