Suggestion for SubstringOrDefault To Avoid Out Of Range Error with Substring Command and Having to First Check Length Is Longer

[robinwilson16]

When transferring data from one system to another or inserting user defined data you may not know how long the resulting string is but if you are inserting into a field that is 100 chars then if <= the max then you want to add it all but if over you may want to insert up to the limit.

For this reason having SubstringOrDefault would be handy and would save you having to only call the function if the string is at least that length to avoid an out of bounds error message.

Here is a definition of what it could look like:

public static class StringFunctions
{
    public static string? SubstringOrDefault(this string? value, int? startIndex)
    {
        string? result;
        if (startIndex == null)
            result = value;
        else if (value?.Length < startIndex)
            result = value;
        else
            result = value?.Substring((int)startIndex);

        return result;
    }

    public static string? SubstringOrDefault(this string? value, int? startIndex, int? length)
    {
        string? result;
        if (startIndex == null)
            result = null;
        else if (value?.Length < startIndex)
            result = value;
        else if (length == null)
            result = value?.Substring((int)startIndex);

        if (value?.Length > length - startIndex)
            result = value?.Substring((int)startIndex!, (int)length!);
        else
            result = value;

        return result;
    }
}

[HaloFour]

API proposals would go to the runtime repository. Sounds like you already have a good solution in that extension method, does it really need to be added to the BCL?

[robinwilson16]

I'm not sure really, I just thought it would be useful if it was available similar to FirstOrDefault so people didn't have to write their own extension methods.

How would I move my proposal to there? Would I need to close it, open a new one and link it from here so new comments go to the new one?
I've had to do another for nullable checkboxes and also nullable select lists and I'm only doing what I thought was a simple input form where I want to ensure values are selected and not defaulted but it's ended up taking longer trying to figure out how to get what I need.

[robinwilson16]

I have just updated the function to account for when start position is less than the total length of the string so it will return the full string instead of returning an error and also made it more compact