You can only use methods without parameters. Implementing parameters is not that trivial.

I've created a substring extension:
`using System;
using System.Collections.Generic;
using SmartFormat.Core.Extensions;
using SmartFormat.Core.Parsing;

namespace SmartFormat.Extensions
{
public class SubstringFormatter : IFormatter
{
public string[] Names { get; set; } = { "substring", "substr", "s", "mid" };

    private char _parametersSepChar = ',';
    public char ParametersSepChar { get { return _parametersSepChar;  } set { _parametersSepChar = value; } }

    public bool TryEvaluateFormat(IFormattingInfo formattingInfo)
    {
        if (formattingInfo.FormatterOptions == "") return false;
        string[] parameters = formattingInfo.FormatterOptions.Split(_parametersSepChar);
        if (parameters.Length < 1) return false;

        object currentValue = formattingInfo.CurrentValue;
        string currentValueString = (currentValue == null) ? "null" : currentValue.ToString();

        int startPos = int.Parse(parameters[0]);
        int length = parameters.Length > 1 ? int.Parse(parameters[1]) : 0;
        if (startPos < 0)
            startPos = currentValueString.Length + startPos;
        if (startPos > currentValueString.Length)
            startPos = currentValueString.Length;
        if (length < 0)
            length = currentValueString.Length - startPos + length;
        if (startPos + length > currentValueString.Length)
            length = 0;
        string substring = parameters.Length > 1 ? currentValueString.Substring(startPos, length) : currentValueString.Substring(startPos);

        formattingInfo.Write(substring);

        return true;
    }
}

}`

Here you can found some examples:
Example: #1: {Person.Name} starts with {Person.Name:s(0,3)} #2: {Person.Name} ends with {Person.Name:substr(-3)} #3: {Person.Name} ends with {Person.Name:substr(5)} #4: {Person.Name} contains {Person.Name:substring(2,-2)} #5: {Person.Name} not contains {Person.Name:mid(20,10)}

Hi, that's very good, thank you!
I plan to add section for contributed extensions in the repo and I'll add yours as soon as time allows.

Do you think your request could be covered with feature request #88 (using RegEx). RegEx will bring about 50% performance penalty, though.

I really like this!
I think substr is a very common use-case, and this extension proves it's pretty simple, so I think it would make sense to include it in the core.
Just my 2¢ ;)

Thanks!

Is there any plan on when another release would be created and pushed to Nuget with this feature included?

Release 2.3.1.0 is published, covering this feature.

Thank you! I appreciate the quick response.